A) The four 8 by 8 blocks of luminance data and the two (for 4:2:0 chroma format), four (for 4:2:2 chroma format) or eight (for 4:4:4 chroma format) corresponding 8 by 8 blocks of chrominance data coming from a 16 by 16 section of the luminance component of the picture.

Macroblock is sometimes used to refer to the pel data and sometimes to the coded representation of the pel values and other data elements defined in the macroblock header. The usage should be clear from the context.

b) The screen area represented by several luminance and colordifference DCT blocks that are all steered by one motion vector. c) The entity used for motion estimation, consisting of four blocks of luminance components and a number of corresponding chrominance components depending on the video format.