When interlaced video is stored in a Frame based format (two fields encoded in a single frame) one Field must consistently be displayed before the other. Which field to display first will depend on their temporal order, meaning which picture was taken first.
The order fields display in is known as Field Dominance or Field Order. It uses varying notation, depending on how the fields themselves are referenced. The most common notation is either TFF (Top Field First) or BFF (Bottom Field First). You may also see variations like UFF (Upper Field First) vs. LFF (Lower Field First).
