What is a sacrifice fly?

It is a fly ball that's hit deep enough to the outfield so a base runner can successfully advance to the next base. The batter is not charged with an at bat, but credited with a sacrifice and does not effect his batting average..When a runner is on 3rd and scores on the play, an RBI is credited to the batter.

A sacrifice fly, in the game of baseball, is a fly ball which was hit in order to allow a runner already on base to further advance.