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. 

Dirt Baggin' It
Condition where a surfer lives a bare-bones existence in order to save every bit of money he makes to spend on his next surf trip.

Diva
Another name for a Wahine or female surfer. Especially one that talented and rips.

Dodgy
Something or someone that's of a suspicious nature.

Doggin'
Going backside in the pit, Green Room, shack, etc.

Doggy Door
The opening between two sections in the lip on a wave that's closing out. Generally it's the best exit point from a wave that closes out. Typically found at sectiony, peaky beach breaks.

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 Overhead
Less than scientific approach to measuring a wave that's two times as tall as a rider.

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.

Drilled
To get axed, dumped, smoked, worked.

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.

Drop in Late
Catching the steepest part of a wave at the waves most critical time.

Drop Knee
Style of body boarding whereby the rider elevates from a prone position at takeoff literally dropping one knee upon the board deck. Modern incarnation of ancient paipoboard riding.

Duckdive 
To duck under a broken wave by pushing the front of your surfboard under the water, then levering the back of the board with pressure from your knee or foot as the wave passes overhead. The desired result is to pass your body and surfboard underneath the powerful whitewater to pop out the back of the wave. Originated by Shaun Tomson and the South Africans in the '70's.