In baseball or softball, a strikeout occurs when a batter accumulates three strikes during a time at bat. It usually means that the batter is out. A strikeout is a statistic recorded for both pitchers and batters, and is denoted by K in scorekeeping and statistics. A "strikeout looking"—in which the batter does not swing and the third strike is called by the umpire—is usually denoted by a Ʞ.

Baseball is a bat-and-ball sport played between two teams of nine players each, taking turns batting and fielding. The game occurs over the course of several plays, with each play generally beginning when a player on the fielding team, called the pitcher, throws a ball that a player on the batting team, called the batter, tries to hit with a bat. The objective of the offensive team is to hit the ball into the field of play, away from the other team's players, allowing its players to run the bases, having them advance counter-clockwise around four bases to score what are called "runs". The objective of the defensive team is to prevent batters from becoming runners, and to prevent runners' advance around the bases. A run is scored when a runner legally advances around the bases in order and touches home plate.