Definitions for fast break
Random House Webster's College Dictionary
(esp. in basketball) a play in which a team that has just regained the ball attempts to score quickly before their opponents reach the other end of the playing area.
Origin of fast break:
(basketball) a rapid dash to get a shot as soon as possible after taking possession of the ball
An offensive play in which a team, having won possession of the ball, moves the ball downcourt as quickly as possible, attempting to get an easy shot before the defense can set up.