In baseball, a grand slam is a home run hit with all three bases occupied by baserunners, thereby scoring four runs—the most possible in one play. According to The Dickson Baseball Dictionary, the term originated in the card game of contract bridge, in which a grand slam involves taking all the possible tricks. The word slam, by itself, usually is connected with a loud sound, particularly of a door being closed with excess force; thus, slamming the door on one's opponent(s), in addition to the bat slamming the ball into a home run.

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.