Accumulation buffer
An extra high-precision image buffer in which several renders of the same scene are summed and averaged into one picture.
Paul Haeberli and Kurt Akeley of Silicon Graphics presented the technique at SIGGRAPH 1990, and it went into OpenGL 1.0 as glAccum. The idea is blunt: render the scene eight or sixteen times with a slightly different camera, moment or light position and add them up. Jitter the camera and you get motion blur or depth of field; move the light and you get soft shadows; nudge by sub-pixels and you get antialiasing.
The cost is equally blunt — N times the render time per frame. 3dfx sold a hardware take on it as the T-buffer in 2000. OpenGL 3.0 deprecated the feature, and today floating-point render targets and TAA do the same job spread across many frames.