Stands for Blind Versus Blind. It is used to indicate a situation that arises when the action folds around to the small blind (SB) who battles it out with the big blind (BB).
Most BvB battles occur in short-handed games because in a full-ring game it is unusual for the action to fold around to the blinds.
EXAMPLE “I flopped two-pair in a BvB battle against a calling station who was willing to play middle-pair for all his chips.”