What "relief pitcher" means in baseball

In baseball, a relief pitcher is a player who comes into the game to pitch for a starting pitcher who needs to rest or who is not performing well. Relief pitchers are sometimes called "bullpen pitchers" because they warm up in the bullpen area of the field. They are different from starting pitchers, who are expected to pitch for several innings and are typically more experienced and skilled. Relief pitchers must be able to perform well under pressure and have a range of pitches to choose from.