AAD - (Automatic Activation Device) A mechanical or electronic device which
automatically opens the reserve parachute at a set altitude as a back up for the user.

Accuracy - Also known as Precision Landing, this is a competition discipline in which the skydiver attempts to land on an established target. At the National level the target is 3 cm in diameter, about the size of a quarter. Accuracy landings of various difficulty, from 20 meters to 2 meters, are required for USPA licenses.

AFF - ( Accelerated Freefall Course). The most advanced method of learning to
skydive.  It is the course that is accelerated, not the speed of the Freefall.  An AFF student receives training on freefall jumps of 40 seconds or longer, accompanied by a qualified jumpmaster, as opposed to Static Line training which does not involve long freefall in the initial training phase. 

AFF CC  - (Accelerated Freefall Jumpmaster Certification Course). This is the
Certification Course that must be successfully completed in order for a
skydiver to be an USPA Accelerated Freefall Jumpmaster. Most Jumpmasters
will tell you it is the most difficult rating to achieve in skydiving.

AGL - (Above Ground Level). Altitudes are in reference either to Ground Level or Sea Mean Level (see MSL). Skydivers always use AGL when referring to altitude. 

Airspeed -  The speed of a flying object through the air, commonly used in reference to aircraft or canopies. 

Altimeter - A device indicating altitude. Looks like a clock face with a single hand. It shows your height above the ground, in thousand foot increments. Audible altimeters beep when you fall through a preset altitude. These are only a backup for a visual
altimeter since if they don't work they don't tell you that they stopped, and if you don't hear them they won't remind you! Audible altimeters are often used by freefall camera people and freestylists since they cannot look at their visual altimeters as often as they'd like.

Angle of attack - The angle at which the wing is presented to the apparent wind. With square parachutes this changes when the brakes are applied. 

Angle of incidence - The angle at which a canopy is trimmed to glide through the air. 

Apparent wind - The wind perceived by an observer. See relative wind. 

Aspect ratio - The ratio of a canopys width (side to side) to breadth (front to back). Seven cell canopies typically have an aspect ratio of about 2.2 to one, while nine cell canopies are usually between 2.8 and 3.0 to one. 


Backslide - To move backward in freefall relative to a neutral reference. Usually unintentional and undesirable, caused by poor body position. 

Bag -  The deployment bag in which the canopy is packed. 

Base - The core around which a formation skydive is built. Can be a single person or a group of people, depending on the number of skydivers involved. 

BASE jump - A jump made from a fixed object rather than an aircraft. BASE is an acronym for building, antennae, spans (bridges) and earth (cliff). 

Beech - Short for Beechcraft, an aircraft manufacturer. Usually used in reference to a Beech D-18, a.k.a. Twin Beech. At one time these were common skydiving planes, but they are becoming obsolete. 

BIC - (Basic instructors course) Attended in an effort to gain a sufficient
level of proficiency with reference to teaching.

BOC - Bottom of container, a deployment system. Refers to the location of the pilot chute. An increasingly common position for main deployment devices, as opposed to belly or leg mounted.

Body position - Ones freefall body posture. Variations in body position are what make a wide range of freefall maneuvers possible.  

Boogie - A gathering of skydivers for a single purpose (skydiving).  This events are usually focused on fun rather than competition. Big drop zones host several boogies a year, often on long holiday weekends. 

Bounce - To land after freefall without the aid of a parachute.  To land at an unsurvivable speed.  Also known as " to frap", or "to go in". 

Box man -  The classic skydive/freefall "belly down" position.  It is a neutral, face to earth body position in which the arms form right angles at shoulder and elbow, and the legs are spread at about 45 degrees from the long axis and bent 45 degrees at the knees. Generally considered the ideal position for Formation Skydiving. 

Brakes - The brake lines of the canopy are synonymous with steering lines. Used together, they slow the parachute. Used independently they result in a turn. 

Break off - To cease formation skydiving by tracking away from the formation prior to deployment. 

Bridle - The thin webbing strap from the pilot chute to the top of the canopy. Part of the deployment system which consists of pilot chute, bag and bridle. 

BSR - (Basic Safety Requirements). BSRs are USPA guidelines. They do not have force of law but are generally regarded as excellent minimum safety standards.

Burble - Area of low air pressure above a descending skydiver caused by a person in freefall or a canopy in flight.. Going into someone else's burble usually results in a frommel.


Call - The time remaining until you are to board the aircraft. For example, a fifteen minute call means you will board in fifteen minutes. 

Canopy - Skydiver talk for a 'Parachute'. See Main Parachute, Reserve
Parachute, Square Parachute, Round Parachute, and Elliptical Parachute.  All of these types of parachutes may be referred to as a canopy.  In simple terms, a canopy is the construction of fabric and lines used to land safely after a freefall.

Cascade - The point where two lines join together so they run smoothly into one. Cascading the suspension lines results in reduced bulk and drag.  

Cells  - The chambers in a ram-air parachute, made up of two halves. They are
delimited by two load bearing ribs and are split in two by the non-load bearing rib in between. Most Skydiving Canopies have either nine or seven cells, but they may have as few as five or many more than nine.  An individual celll may be split into more than two parts. A nine Cell Canopy is generally a more efficient wing than a seven cell because it has more ribs and can be a better airfoil.  Note that canopies with more cells have more ribs and more fabric -- they do not pack as small.

Center point - The point around which movement takes place. In an individual the center point is considered to be in the middle of the torso. In a group, it is the point that the formation centers around. 

Chute assis - French for sit flying, or freefalling with one's seat presented to the relative wind. 

Closing loop - The small loop that holds the flaps of the container closed once the pin has been guided through the loop. 

Coach - A skydiver with some formal training in the art of instructing freefall technique. 

Container - The part of a Rig which contains the Main and Reserve Parachutes.

Crabbing - A canopy is crabbing when it is flown at an angle sideways to the ambient wind, resulting in a path across the ground that is sideways as well as forwards. 

Creep - To creep is to practice formation skydiving sequences while laying prone on a creeper. 

Creeper - A board equipped with wheels on which a skydiver lays to simulate freefall maneuvers. 

Cross ports - Holes in the ribs of a cell that allow air to flow from one cell to another. 

CRW - (Canopy Relative Work).  Now officially known as Canopy Formations. CRW involves flying open canopies in close formation, where the pilots actually take grips on each other's parachutes. 

Current - To "be current" is to have jumped recently enough to retain proficiency in the sport. Uncurrent skydivers, depending on their experience, must be supervised to some degree when they resume jumping. See the SIM. 

Cut away - To release the main parachute, cutting away is a standard emergency procedure prior to deploying the reserve. More properly known as a breakaway, the technique involves using a simple release system activated by pulling a handle. In some systems, the cut away or breakaway system will also automatically deploy the reserve canopy.

CYPRES - A type of AAD. Made by AirTec of Germany, this is the most common type of AAD and the first modern design to be widely adopted by expert skydivers. 


DC-3 - A type of aircraft, the Douglas DC-3 is a large, twin engined airplane capable of carrying over 40 jumpers. Like the Twin Beech, DC-3s are being rapidly replaced by more modern turbine engined aircraft. 

De-arch. To flatten out or reverse one's body position from the normal arched box man. A de-arch results in a slower fall rate than an arch. 

Dacron - A common construction material for canopy suspension lines. Dacron lines are thicker and softer than so called "microlines". 

Data card - Every parachute carries a data card with information on the reserve parachute, including type, last date packed, owner, serial number, etc. 

Dead spider - Slang for de-arch. 

Decision altitude - The altitude at which a skydiver is trained to begin execution of emergency procedures. Usually 2,500 feet AGL for students, and 1,800 feet for expert skydivers. The decision altitude may be higher depending upon the expertise or comfort of the skydiver. 

Delta - A body position which forms somewhat of an arrow shape.

Deployment system - The components of the parachute that control deployment of the canopy. Includes pilot chute, bridle and bag. 

Dirt dive - To rehearse a skydive on the ground. 

Dive floater - A dive floater is a skydiver who is inside the airplane in the exit line up, but leaving prior to the base. This configuration only occurs on large formations. 

Dive loops - Many advanced skydivers have loops or "blocks" on their front risers to make it easy to grip the front risers for steering purposes. Also called front riser loops. 

Diver - Anyone diving out of the plane during a formation skydiving exit. 

Door jam - To practice an exit in the aircraft door of a mock up of it prior to the skydive. 

Down plane - A CRW formation with two canopies, both pointed toward the ground. This can also occur to a single skydiver with both main and reserve deployed. 

Drop zone - Common slang for a skydiving center, also DZ. 

Dytter - A common brand of audible altimeter. 


Elliptical Parachute - A wing shape characterized by a tapering leading and trailing edge so that the middle of the canopy is wider, front to back, than the ends. This configuration is typical of many high performance canopies.  These Canopies are far more radical than Square parachutes capable of doing 360 degree turns in 1-2 seconds, with the Skydiver and Parachute parallel to the ground. There are variations between Square and Elliptical, some called Semi-Elliptical.

End cell - The cell furthest out on a canopy. 

Exit weight - The total weight of the jumper and all equipment and clothing. 


F-111 - A fabric common in mid range canopies, F-111 is slightly permeable to air and wears faster than zero-p fabric. Pronounced "F one eleven".

FAA - ( Federal Aviation Administration)  The agency of the US government that regulates aviation activity, including skydiving.

FAI - ( Federation Aeronautique Internationale) The international body which
administers sport aviation throughout the world.

FARs - Federal Aviation Regulations, the laws governing aviation. 

Fall Rate - The rate at which you fall, another name for terminal velocity
except that it refers the rate relative to other jumpers rather than an
absolute velocity. Fall rate is adjusted by adjusting body position.
Different shape and weight jumpers in exactly the same body position will
fall at different rates. Fall rate must be adjusted to be the same as
everyone else so that the jumper can do Relative Work.

Flare - The act of pulling down the brakes of the canopy in order to slow it down, resulting in an increased angle of attack and reduced descent rate. 

Floater - Skydivers who leave the airplane before the base are called floaters since they must use a slow fall rate to get up to the base. Floating also refers to an exit position outside the airplane. 

Formation - When referring to Relative Work a formation is a group of skydivers forming particular pattern by taking grips on each others arms and legs. The
formations that will be done on a jump are determined and practiced (Dirt
Dived) before the jump. When referring to Canopy Relative Work, it is a formation of Canopies flying together in a predetermined configuration.

FS - (Formation Skydiving)  Skydiving discipline in which two or more skydivers join together in different positions to make different formations.  (Previously known as relative work).

Freestyle - A type of skydiving characterized by acrobatic individual flying, reminiscent of gymnastics.  (Formation skydiving stalwarts reckon this is just because they can't get stable.)

Frommel - What happens when a skydive formation self destructs.

Funnel - A funnel occurs when one or more skydivers find themselves in an unstable body position and end up in a skydivers burble. The resulting loss of stability for the other skydivers usually causes the formation to break up.


Glide ratio - The distance a canopy flies forward compared to down. A canopy with a 3:1 glide ratio flies three feet forward for every foot of vertical descent. 

GPS - (Global Positioning System) By picking up signals from satellites, a GPS receiver can tell the user position over the ground. Used in skydiving aircraft to spot the exit. 

Grips - (or grippers) Using the hands to hold onto another skydiver in freefall or during the aircraft exits. In formation skydiving, the formations are scored as complete when every skydiver has taken the correct grips. Can also refer to the sausage shaped devices or material  attached to the arms and legs of a jumpsuit for skydivers to hold on to in formations.

Ground speed. The speed of an airplane or skydiver over the ground, as opposed to through the air. 


Hacky - Game in which a group of skydivers attempt to keep a small hacksack (beanbag) in the air for as long as possible by kicking it. Breaking any of the myriad of obscure but sacred hacking rules results in the offending skydiver having his bum kicked by the rest of the hackers. Also known as "A game played with a ball that doesn't bounce by people who might".

Hand deploy - To activate the parachute by manually deploying the pilot chute as opposed to pulling a ripcord. 

Harness - The part of a Rig which consists of webbing and metal hardware which
you wear and which the Container is attached to.

Heading - The direction an aircraft, skydiver, or parachute is facing. The ability to recognize and maintain heading is crucial to jumping with others successfully. "On" or "off" heading are terms commonly used to describe exits and deployments. 

Holding - When a parachute is flying directly into the ambient wind, it is said to be holding. See running and crabbing. 

Hook knife - A small knife carried in the jumpsuit or on the parachute harness, the hook knife is designed to cut lines or webbing. A small razor blade is recessed in a hook shaped handle to prevent unintentional cuts.

Hook turn - A sudden turn close to the ground (90 degrees or more) used to build up speed for a spectacular turf surf and gentle landing. When misjudged can result in smashed bones and a lengthy stay in the hospital.

Hot fuel - When the airplane does not shut down during fueling. Do not board the aircraft while fueling is in progress. 


ICC : (Instructor Certification Course) The course one must attend and
successfully pass in order to obtain an instructor rating.

In date - A reserve packed within the previous 120 days is said to be "in date". If more than 120 days have elapsed since the reserve was packed it is"out of date" and illegal to use. 

Instructor - Someone who has held a USPA jumpmaster rating for at least one year and passed an Instructor Certification Course. 

IPC - (International Parachuting Commission) This commission oversees sport parachuting. It is a committee of the FAI. 


Jump run - The flight path taken by the jump plane to put the skydivers in position over the airport. 

Jumpsuit - A cover all type garment designed for specific skydiving applications such as FS, freestyle or accuracy. 

Jumpmaster - Someone who has successfully attended a USPA Jumpmaster Certification Course. A jumpmaster has all of the privileges of an Instructor except that they cannot supervise a first jump course, sign off licenses, or manage a student program without an instructor's supervision. 


Key - A signal to move on to the next step in a skydive. 

King Air - A turbine aircraft made by Beechcraft and common in medium sized drop zones. 


Line of flight. An imaginary line corresponding to the jump plane's path over the ground, the line of flight is a useful reference line on larger formation skydives. Also, during the jump run the skydivers will be distributed along this line of flight. 

Log book - Like pilots or sailors, skydivers log their activity and achievements in order to document their experience. 

LORAN - A navigational system similar to GPS except based on ground transmitters, LORAN is relatively obsolete. 


MSL - (Mean sea level). Used by pilots when defining altitude, MSL refers to feet above sea level as opposed to above the ground. Pilots always use MSL when referring to altitude. 

Main Parachute - The parachute you use first. If it doesn't work you use your
Reserve. This happens very rarely and there are Skydivers with thousands of
jumps and no Reserve rides. The Main parachute is usually much higher
performance than the Reserve. There are many types and brands available, in
custom colors for no extra cost if you want, and they come in all sizes from
69 sqft 9+ Cell parachutes, for very small, light and/or highly experienced
Skydivers, to 280-300 sqft 7 or 9 Cells that students usually use, to 520
sqft 9+ Cells for large Tandem parachutes. These are all Square parachutes.
Round parachutes are typically only used as mains for special applications - water
jumps and Pilots Rigs, for example.

Mal - Shorthand for Malfunction.

Malfunction - When the Main Parachute doesn't work properly. There are
different degrees of malfunctions, the bad ones of which cause you to use
your Reserve.

Manifest - 1) The list of skydivers on the jump plane. 2) The act of going to the office where this list is maintained to put yourself on a plane. 3) The location where manifesting takes place. 

Microline - A modern type of suspension line considerably smaller than dacron line. 



Organizer - Someone with leadership skills and skydiving expertise who plans formation skydives or event functions.

Otter - The DeHavilland Twin Otter, a very popular turbine jump ship carrying up to 23 jumpers. 

Out landing - Landing off target. 

Out of date - See in date. 


Packing data card - See data card. 

Parachutist - A person who uses a parachute. A Parachutist is not necessarily
a Skydiver. A Skydiver is only a Parachutist because they have to be. Note
for non-jumpers: do not call a Skydiver a Parachutist and don't ask them
about 'their Parachuting'.

Peas -  Pea gravel, used in the landing area as a target reference and because it is forgiving of hard landings. 

Pilot - A person who likes planes but usually does not jump out of them. 

Pilot Chute - Small parachute attached to the main parachute that is used to remove the main from the harness and fill it with air.

Pin - 1) The skydiver who first gets to the base. Base/pin are the two people around which many formations are built. 2) The act of docking on the base. 3) The closing pin of the main or reserve container, which should both be checked prior to jumping. 

Pit - The pea gravel area.

PLF - (Parachute landing fall). A technique used to minimize injury during rough landings, a PLF distributes the landing shock along feet, calves, thighs, hip and shoulder. 

Porter - A single engined turbine aircraft carrying up to ten jumpers. 

Post dive - Review of a skydive after everyone has landed. 

PRO rating - A USPA rating indicating competence to perform difficult demonstration jumps. 

Pull out - A type of hand deploy pilot chute where the pilot chute is packed inside the container and pulled out using a handle with a lanyard to the pilot chute. 

Pull up cord - A piece of cord or line used to pull the closing loop through the grommets of the container. 

Pud - Slang for the handle on a pull out pilot chute system. 




RSL - Reserve Static Line, a backup device for automatically deploying the reserve if the skydiver cuts away their main canopy.  Note: this system is only effective in malfunctions where the main is at least partially deployed.

RW - (Relative Work) Now known as Formation Skydiving.  Skydivers in
freefall link up to create formations. This can be done in any numbers from
2-person (called a 2 Way Skydive) and up. Competition RW is mainly done in 4
person teams (4 Way Teams) and in 8 Ways & 16 Ways.

Ram air - A modern "square" parachute, these inflate with air and take on a aerodynamic profile, much like an aircraft's wing, allowing them to be flown rather than just descending like an old style round parachute.

Relative wind - The apparent wind felt by a jumper in freefall, relative wind is the result of the skydiver's speed through the air. 

Reserve Parachute - The parachute you use if your main parachute mals. Reserve
parachutes must be tested to very strict standards & must be inspected and
repacked by a specially licensed packer at regular intervals, whether they have been used or not.

Reserve Ride - To use the Reserve Parachute.

Rig - What you would think of as 'the parachute' in the phrase 'To wear a
parachute'. Consists of a Harness, Container, Main Parachute, Reserve
Parachute and the means of deploying each parachute.

Rigger - Someone with a certificate from the FAA stating they have successfully met the requirements to be a parachute rigger. 

Rigger's certificate - The certificate possessed by a rigger as proof of competence. Senior riggers may make minor repairs and pack reserve and main parachutes. Master riggers may make major repairs and alterations as well as packing parachutes. 

Rip Cord - The small handle used to deploy a spring loaded pilot chute on a freefall rig. Many expert rigs use a throwout or pull out pilot chute instead.

Risers - The webbing that connects the harness to the suspension lines. At the bottom of the risers will be a mechanism for attaching and releasing the risers and harness, usually in the form of a three ring release. On the rear risers are the brakes/steering lines. The suspension lines attach to the top of the risers with connector links, also known as rapid links. 

Round -  1) A formation where each skydiver has grips on the arms of those next to him, also known as a star. 2) Shorthand for "Round Parachute".

Round Parachute - A round parachute.  These range from non-steerable to a bit steer able and the user is mainly at the mercy of the wind. Cannot really be flared and give fairly hard landings. Works by providing drag to slow the descent of the Skydiver.

Running - When a canopy is flying with the ambient wind it is said to be running. This produces the greatest possible ground speed. 


S&TA - Safety and Training Advisor. The S&TA is a volunteer representative of USPA who attempts to disseminate information about safety and act as a liaison between the DZ and USPA. Most S&TAs hold instructor ratings. 

SCR - The oldest award for formation skydiving achievement, for those who have been in a star of at least eight people in which each person left the aircraft separately and flew to the formation. 

SIM - (Skydiver's Information Manual) Published by the USPA, the SIM is a comprehensive manual on USPA policies and training methods. It also includes FARs pertinent to skydiving. 

SOS - (Single Operation System). This system simplifies emergency procedures by combining the functions of the cut away and reserve handles in a single handle. 

Seal - Reserve parachutes have a small lead seal on a piece of red thread around the closing pin. This seal indicates the reserve has not been opened since it left the riggers hands. 

Sentinel - A type of AAD. 

Single operation system - See SOS. 

Skygod - Although on the surface this term refers to a superior skydiver, in drop zone use skygod is a derogatory term for a skydiver whose ego and maneuvers have grown faster than his or her skydiving ability. 

Sky Shark - A derogatory term for an unwelcome aircraft in a drop zone area.

Slider - A rectangular piece of nylon fabric with a grommet at each corner through which the canopy's suspension lines are routed. Packed at the top of the lines, the slider controls the opening of the canopy by preventing the parachute from expanding too rapidly. 

Slot - A position in the skydive or on the plane. Uses: "dock in your slot", or "two slots left on the next Otter". 

Spectra - A material from which microline is made. 

Spot - The position of the aircraft when the jumpers exit. Spotting duties (selecting the spot) can be done by a skydiver or the pilot. 

Square Parachute - An airfoil shaped ram-air parachute which is actually rectangular with aspect ratio's from less that 2 up to more than 3.5. The parachute is termed a 'semi rigid wing'. It is held in a wing shape by the air rushing in the front, keeping it pressurized. Squares work not by providing drag to slow the descent but by providing lift as they fly at about a 3:1 glide angle. They therefore must fly quite fast! Speeds up to 40-50mph in a straight line depending on the Canopy and the weight of the Skydiver are possible! They can be flown into the ground at in excess of 80 mph if one wants to.  The most common configurations are 7 and 9 Cells and they can be made of porous material or non-porous Zero Porosity material.

Stabilizer. The vertical strips of cloth depending from the end cells of the canopy. Stabilizers improve the canopy's ability to fly straight ahead and enhance efficiency by reducing tip vortices. 

Stall - When the angle of attack of a wing becomes too high to sustain lift, the wing is said to be stalled. 

Static Line - A line attaching the parachute to the plane, used to automatically deploy the parachute as soon as the parachutist exits the plane. Used to train students.

Steering lines - The lines that run from the steering toggles on the rear risers to the trailing edge of the parachute. 

Steering toggles - Handles attached to the end of the steering lines to facilitate their use. Toggles and lines are configured so they can be stowed in a partially down position to enhance the opening of the parachute. 

Stow - To neatly arrange suspension lines on the deployment bag or steering toggles in their position on the rear risers. 

Style - A type of freefall competition where an individual skydiver attempts to execute a predetermined sequence of maneuvers in the shortest possible time. 

Suspension lines - The lines from the risers to the canopy. They are normally in four groups, labeled from front to back as A, B, C and D. They can be further divided into right and left or front and back riser groups, and by type of material. 

Swoop - 1) To dive down to a formation or individual in freefall. 2) To aggressively approach the landing area in order to produce a long, flat flare and an exciting landing. 


TSO - (Technical Standard Order) A technical standard that all American parachutes must meet before they can be marketed. Unless specifically exempted by the FAA, a parachute must have a TSO placard to be legal. 

Tandem Skydiving - A common first jump method. In some training methods, also used until the Assisted Freefall phase.  The passenger and Instructor are harnessed together and use a the same main parachute, the student may participate very little in the actual jump or control.

Terminal Velocity - The speed at which a Skydiver falls when the friction of
the air on their body is equal to and counter acts the force of gravity so that they no longer accelerate. It is about 120 mph in a flat stable position, lying on the air, face down. The Skydiver can fall faster or slower, up to a point, by changing their body position.

Three ring - A parachute release mechanism that utilizes three rings of separate size in a mechanical advantage system. Invented by Bill Booth in the late 70s, the three ring release is almost universally considered the best cut away system available. 

Throw Out - A type of pilot chute that the skydiver actually throws into the air rather than an old style spring loaded pilot chute.

Toggles - Handles on the steering lines. 

Track - To track is to assume a body position which gives a very high horizontal speed.

Turf Surf - A long, flat skim across the grass and gentle landing that follows a properly timed and executed high performance landing (see hookturn) . When mistimed the result is a turf eat.

Turn around load - When the aircraft does not shut down between loads, but lands and picks up skydivers for immediate departure. 


USPA - United States Parachute Association

Uppers - The upper winds, or winds at exit altitude. The "uppers" are often much stronger and occasionally from a different direction than ground winds. 



Wave off - Prior to deployment a skydiver should make a clearly defined arm motion to indicate to others nearby that he is about to open his parachute. A good wave off is essential to the avoidance of deployment collisions. 

WDI - (Wind drift indicator). A paper streamer thrown from the jump plane to estimate winds under canopy and determine the spot. 

Weights - Many lighter skydivers wear a weight vest to allow them to maintain a fast fall rate. 

Whuffo - Derogatory term for a non-jumper, comes from the typical non-jumper question "What for you want to jump out of a perfectly good airplane?" to which of course the answer is "because the door was open".

Wind line - An imaginary line from the desired landing area, extending directly along the direction the wind is blowing. 

Winds aloft - See uppers. 

Wing loading - The ratio of weight born by a wing to its surface area. In the US, divide your exit weight in pounds by the square footage of the canopy. 


ZP/Zero-P - (Zero Porosity) Non-porous to air. (Not technically the
correct term, but it's the one Skydivers use). Air does not go through it
making ZP Canopies very efficient wings.