To become stuck or make something become stuck, preventing movement. The paper jammed in the printer, causing a delay in printing.
To fill a space tightly with a large number of people or things. Fans jammed the stadium to watch the championship game.
To play music informally with other musicians, often in an impromptu manner. The band members decided to jam together after the concert.
To interfere with or block a signal, such as radio or radar, by sending out a different signal. The military used electronic warfare to jam the enemy's communications.
To injure (a finger, toe, etc.) by sudden compression or impact. He jammed his index finger while catching the basketball.