Editing
B-Roll
Supplemental or alternative footage intercut with the main shot.
In Depth
B-Roll is used to add visual interest, cover edits (jump cuts), or provide context to what is being said in the A-Roll. Without B-Roll, a video would just be a talking head.
Example
"While the chef describes the dish (A-Roll), we see shots of chopping onions and sizzling pans (B-Roll)."