Deck
The top surface of a surfboard on which you apply wax for traction.

Deck Grip
Rough-surfaced material patch, usually a fraction of an inch thick, which can be glued to the deck of a surfboard to increase traction instead of wax. Surfing A-Z

Deep Water
Water deep enough so that surface waves are not affected by the bathymetry on the ocean bottom. Generally, water more than 1,000 feet, or at least deeper than one-half the wavelength of the existing waves is considered deep water.

Deepwater breaks
Surf spots where the swells have a steep transition from deep water to shallow water so the waves are generally bigger and more powerful than elsewhere. Also includes surf spots where the deep water bathymetry of the ocean floor can greatly focus longer period swells (over 16 seconds) to create larger and more powerful waves. Spots with underwater canyons like Blacks are a prime example.

Degrees 
A) The unit of measurement for direction to analyze where wind and swell direction is coming from. North is 0 or 360 degrees (12:00 o'clock); and then moving clockwise, east at 90 degrees (3:00 o'clock), south at 180 degrees (6:00 o'clock) and west at 270 degrees (9:00 o'clock). Northeast may be anywhere between 0 and 90 degrees, southeast between 90 and 180 degrees, southwest between 180 and 270 degrees and northwest between 270 and 360 degrees. B) Degrees also are used to measure Latitude and Longitude, with minutes and seconds used a fractionals between the degrees. One degree of Latitude will always equal 60 miles at that same location. One degree of Longitude will always vary due to the curvature of the Earth toward the poles.

Designer
An expert surfboard shaper or rider who originates ideas for surfboard shapes. See shaper.

Diffraction
The process of wave energy filtering into the lee of obstacles such as breakwaters by the transfer of the wave energy along wave crests. Diffracted waves are smaller than the original waves.

Ding
Damage to surfboard caused by dropping or collision with another hard object or surfboard. Dings must be dried out and repaired immediately otherwise water will weaken the strength of the board.

Direction
Where the wind or swell is coming from. In the marine community, directions are always identified as the direction the swell or the wind is "coming from," not the direction it's headed. Surfline uses directions in true degrees as:

Double blindstitched
Seam is glued together and blindstitched on the outside, turned inside out and blindstitched on the inside; considered a very watertight seal.

Double up
When two waves combine, often creating an extra powerful wave with twice the amount of energy. Double up waves often create the best waves to get barreled or tubed on because the interaction of the waves forces the waves to break in shallower water than normal, which creates hollower, steeper waves.

Down Rail
A rail (see rail) shape in which the deck slopes down to meet the bottom, rather than vice versa. Credited to Mike Diffenderfer of the USA in the 1960s.

Down-the-line
A reference to the direction further along the crest of a wave from the location from where a surfer drops into the wave. The direction toward which the surfer is riding. Waves can also be described as "down-the-line" when the wall is long and fast.

Drag
The effect that causes water flow to be slowed or disrupted as it passes along a surfboard's surfaces. Causes of drag are usually present in the leading edges of a surfboard: the forward rail line, the forward rocker and outline, and the leading edges of fins, and in bottom features which cause water resistance, such as tail vee. Controlled drag is an essential requirement of surfboard design.

Drive
The effect of water pressure pushed against a surfboard's surface, which creates acceleration down the line on a wave. This is the simple way of describing drive and its immediate effect. Looking at it more closely, we see that "drive" in a surfboard context implies a couple of factors. - First, it's about pressure. Specifically, water pressure working against a surface. To harness the pressure, you've gotta have a surface for it to work against (ie., a fin). - Second, it's about direction. Drive is aimed; it's purposeful, not random. Drive doesn't have an opposite so much as a corollary, which is Drag. Drag results from friction between waterflow and wetted surface, and it's not altogether a bad thing; without some elements of Drag, as without Drive, a surfboard would be virtually impossible to control. (Best example I can think of: a surfboard without any fins at all.) Almost without fail, wherever you create the possibility of Drive, you'll also have the possibility of Drag. Getting that balance right is the key to great surfboard design. A middle fin adds Drive and Drag at a central point of a surfboard's tail. This adds control and direction, providing an anchor for turns. In the classic Thruster setup, the side fins are reduced in volume in order to balance the design. Take the middle fin away, and both Drive and Drag are removed; waterflow gets past the fins more easily, giving the board a skatier, skimmier feel, but some control and direction is lost. This is only partially made up for by the larger fin size of the classic Twin-fin design.

Drop
The initial part of a ride when a surfer slides down the face of the wave.

Drop-in
 When a surfer initially goes down the face of the wave after catching a wave. Also a term used to describe catching a wave in front of another surfer who is already riding, which is a general breach of surfing etiquette.

Dumping
Used to describe waves that are very hollow and hard-breaking.

Duration
In wave forecasting, the length of time the wind blows in the same direction over the swell generating area, or the fetch. Duration is one of the three key elements in the fundamental wave generation formula-along with wind velocity and fetch length-used to determine wave heights and wave periods in a storm or wave generating area.

Channel
Bottom shape dating back to 1970, credited to Jim Pollard of Australia, in which grooves are cut lengthwise along the surfboard, usually through the tail half. Many different types of channels have a variety of effects on performance; generally they add drive and direction to turns, especially in the most common modern variation, the six-channel "clinker" bottom.

Choppy
Bumpy ocean and wave conditions that are rough due to strong winds and/or currents. Wind velocities are usually over 12 knots to create choppy conditions.

Clean
Good surfing conditions with decent wave energy, a smooth or glassy ocean surface and very little onshore wind. Offshore winds blowing into the faces of the waves can create clean, groomed conditions.

Clean-up set
A much larger wave or a set of waves, which breaks further outside than normal. A clean-up set usually "cleans" the line-up of surfers caught further inside.

Climbing and dropping
Turning up and down the face of a wave as you surf down the line. A very good technique for gaining speed with each turn.

Closeout
 When all parts of the wave-down the line or crest of the wave-break at the same time. (Opposite of closeouts, the ideal waves for surfing are ones that break from one side to the other so the surfer can angle across the face of the wave.)

Computer
("computer board", "computer shape") Many top shapers currently use highly accurate machines to cut blanks into near-ready shapes, or "pre-shapes". These are driven by computer programs, which use data from the shapers' prototype designs (see "plug"). The computer has reduced man-hours on a shape job to as little as 15 minutes.

Concave
Design feature involving a slight scooping out of an area of the board, usually the bottom from rail to rail, during the shaping process. Concave is a paradox because it provides both lift (a skatey freeing up of the board) and drive (from pressure on the water along the exit rail).

Consistent
A surf condition when waves are coming in very frequently and in predictable quantities.

Continental Shelf
The underwater shelf extending from a continent out to sea to a depth of about 165 fathoms or 1,000 feet. Long period swells of about 20 seconds will begin to feel the ocean floor at about 1,000 feet.

Contour
A line on a map or chart representing points of equal value compared to datum or starting point. An isobath is a line connecting points of equal depth below a datum to measure bathymetry, and an isobar when used to represent atmospheric pressure.

Corduroy
Describes the vision of a series of swells marching in from the horizon.

Corners
The end sections or shoulders of waves. A term usually used on the more closed out days when surfers try to find shoulders or corners to ride.

Crease
Damage to a surfboard caused by heavy general impact, in which the surfboard flexes further than the glass and resin allows. Usually indicated by a fracture line running across the board on bottom, deck or both. A bad crease may shatter glass around the rail and lead to a complete break in the affected board.

Crest 
The top part or lip of the wave or swell.

Cyclone
An atmospheric closed circulation rotating counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Can be a high-pressure or low-pressure cyclone.