a batter who didn't start and didn't play in the field yet and is batting for another player
a designated player who will come in at a certain stage of the innings to speed up the scoring of the runs
A hitter who replaces another player during his Plate Appearance. The original batter can't return to the game, so the pinch hitter or a third person takes over the defensive position as well.
A player who bats in place of a team-mate one time in a game.
A hitter who substitutes in the line-up for a starting player. The original batter can't return to the game, so the pinch hitter or a third person takes over the defensive position as well.
a batsman known for batting aggressively, who comes in to bat above his normal batting position expressly to score runs quickly, possibly at the expense of his own wicket. The term comes from baseball, but has been adopted for a different meaning.
In baseball, a pinch hitter is a common term for a substitute batter. Batters can be substituted in at any time while the ball is dead (not in active play); the manager may use any player that has not yet entered the game as a substitute. This is called defensive substitution.
In cricket, pinch hitter is the usual term for a batsman (not a substitute, unlike in baseball) promoted up the batting order in order to score quick runs. As scoring runs quickly makes a batsman more likely to get out, it is generally considered unwise for a top-order batsman to attempt this. Therefore, on the fall of a wicket, a lower-order batsman (such as a bowler) is sometimes promoted.