In an interlaced video a field is 1/2 of a complete picture (Frame) consisting of the even or odd scanlines in the frame. Usually each field is labeled ie. Field A and Field B. When working with interlaced video it is important to note the Field Order (if Field A comes before Field B in the video stream) especially when encoding. If you notice flicker after encoding you will want to change the field order in the encoding template and reencode.