A) Technique for increasing picture repetition rate without increasing base bandwidth by dividing a frame into sequential fields. When first introduced, it also had the characteristic of making the scanning structure much less visible. NTSC uses 2:1 interlace (two fields per frame).

b) A process in which the picture is split into two fields by sending all the odd-numbered lines to field one and all the even-numbered lines to field two. This was necessary when there was not enough bandwidth to send a complete frame fast enough to create a non-flickering image.