In basketball, a shot players take with the time running out. It's usually a "hey, maybe the luck turns to me" shot but they might also decide the winner. Of course, most of the buzzerbeaters miss, because they're very difficult. The most famous buzzerbeaters are loooong range 3-pointers that go in, again, usually with some help of luck. By the way: the ball must be released from a player's hands before the buzzer sounds.
(real situation, youtube it)
(crowd): BEAT L.A., BEAT L.A....
Lakers inbound it, Kobe Bryant comes from under the basket, catches the ball on the 3-point line and shoots the ball which hits nothing but net.
the reporter: Whoooo! Are you kidding me? A buzzerbeater by Kobe and the Lakers win this one in double OT...