Macroblock

Fundamental working unit of the MPEG compression system that contains a 16 16-pixel portion of one frame or field of a video sequence. The term macroblocking is often used to describe a deteriorated MPEG image in which portions of the image have been replaced with single color blocks that occupy a 16 16-pixel portion of the displayed image; this is normally caused by missing or corrupt data in a compressed video stream that is being processed
by an MPEG decoder.