What Constitutes a Save in Baseball?

In order to be credited with a save, a pitcher needs to be the finishing pitcher on the winning team, and not be the winning pitcher. In addition, he needs to pitch at least 1/3 of an inning. He also needs to satisfy one of the following: enters the game with no more than a 3 run lead, enters the game with the tying run either on base, at bat, or on deck, or he pitches for at least 3 innings.