intransitive verb1 a: to become blocked or wedged b: to become unworkable through the jamming of a movable part 2: to force one's way into a restricted space 3: to take part in a jam session 4:dunk 2transitive verb1 a: to press into a close or tight position <jam his hat on>b (1): to cause to become wedged so as to be unworkable <jam the typewriter keys>(2): to make unworkable by jamming c: to block passage of :obstructd: to fill often to excess :pack<the crowd jammed the theater> 2: to push forcibly; especially: to apply (brakes) suddenly and forcibly —used with on 3:crush, bruise 4 a: to make unintelligible by sending out interfering signals or messages b: to make (as a radar apparatus) ineffective by jamming signals or by causing reflection of radar waves 5: to block, crowd, or bump (a pass receiver) near the line of scrimmage in football 6: to pitch inside to (a batter)