## O

odd field
  The first field comprising a video frame in an odd/even field set.
off-screen surface
  A conceptually rectangular area in memory that is generally used to store bitmaps that will be blitted to a back buffer before being displayed. Commonly used to store sprites.
opcode
  Operation code that defines how the vertices in an execute buffer should be interpreted or how the state of the system should be changed.
overdraw
  The average number of times to which a screen pixel is written.
overlay surface
  A conceptually rectangular area in memory whose stored image information will cover the image information of the primary surface to which it is applied. Overlays are assumed to be on top of all other screen components.
overlay z-order
  Determines the order in which overlays clip each other, enabling a hardware sprite system to be implemented under DirectDraw.