D

Depth of Field : The distance between the closest and farthest objects in focus within a scene as viewed by a lens at a particular focus.
Diffuse : Light that is reflected from an object's surface, regardless of the angle from witch its viewed.
Dissolve : An animation effect that is a transition between two sequences involving a fade from one directly to the other.
Dither : The mixing of adjacent pixels to simulate additional colors when available colors are limited, such as on an 8-bit monitor or an 8-bit palette.
Dithering : One of many processes for reducing the total number of colors present in an image while retaining visual fidelity. Dithering can be done by interleaving pixels of selected colors to locally approximate the desired color. Dithering can be applied to either a color or a grayscale color space and may be necessary due to a limited number of colors available on the display device.
Dodge : To bleach (lighten) an area of an image.

DPI : (Dots per inch) A unit that is used to measure the resolution of a printer or image setter. Dpi is sometimes used to describe the input resolution of a scanner, but "ppi" is the more accurate term.
Duotone : A grayscale image that is printed using two plates to enhance its tonal depth.