A card that does not block certain key combinations in a player’s range. For example, holding 33 on K73 unblocks top and second pair, which makes it more likely to get action. Facing a larger river bet on JT652 while holding AA unblocks missed (A-high) flush draws and unblocks a lot of missed straight draws, which improve the probability that the opponent is bluffing. The reverse also applies. See: Blocker.