A series of macroblocks, all placed within the same row horizontally.

Slices are not allowed to overlap. The division of slices may vary from picture to picture. If “restricted slice structure” is applied, the slices must cover the whole picture. If “restricted slice structure” is not applied, the decoder will have to decide what to do with that part of the picture which is not covered by a slice. Motion vectors are not allowed to point at the part of the picture, which is not covered by a slice. Note that Main Profile uses “restricted slice structure,” that is, all the slices put together must cover the picture.