A walk-off in baseball is any offensive play that gives the home team the lead in the bottom of the last inning, resulting in an immediate victory. This can occur in the bottom of the ninth inning or extra innings, and the visiting team will not get another turn at-bat. A walk-off can be recorded in many ways, including a hit, an error, a walk with the bases loaded, a hit by pitch with the bases loaded, a sacrifice fly, an out (with less than two outs in the inning), a wild pitch, a passed ball, and a balk. As long as enough runs are scored to end the game as the result of the play, it is considered a walk-off.

Walk-off celebrations typically consist of an entire baseball team leaving the dugout to meet a player at home plate after the batter hits a walk-off home run, or at whichever base the hitter happens to reach if a traditional base hit results in a walk-off victory. The term "walk-off" originated as "walk-off piece," and was coined by Hall of Famer Dennis Eckersley. It was originally intended to describe a pitchers dejected walk off the field after giving up a game-losing home run, but it soon grew into its own phenomenon.