jam¹ / jam/ • v. (jammed , jam·ming ) 1. [tr.] squeeze or pack (someone or something) tightly into a specified space: four of us were jammed in one compartment people jammed their belongings into cars. ∎  push (something) roughly and forcibly into position or a space: he jammed his hat on. ∎  [tr.] crowd onto (a road) so as to block it: the roads were jammed with traffic. ∎  [tr.] cause (telephone lines) to be continuously busy with a large number of calls: listeners jammed WBOQ's switchboard with calls. ∎  [intr.] push or crowd into an area or space: 75,000 refugees jammed into a stadium today to denounce the accord. 2. become or make unable to move or work due to a part seizing or becoming stuck: [intr.] the photocopier jammed | [tr.] the doors were jammed open. ∎  [tr.] make (a radio transmission) unintelligible by causing interference. 3. [intr.] inf. improvise with other musicians, esp. in jazz or blues: the opportunity to jam with Atlanta blues musicians.• n. 1. an instance of a machine or thing seizing or becoming stuck: paper jams. ∎ inf. an awkward situation or predicament: I'm in a jam. ∎ short for traffic jam. ∎  Climbing a handhold obtained by stuffing a part of the body such as a hand or foot into a crack in the rock. 2. (also jam ses·sion) an informal gathering of musicians improvising together, esp. in jazz or blues.PHRASES: jam on the brakes operate the brakes of a vehicle suddenly and forcibly, typically in an emergency.jam² • n. a sweet spread or preserve made from fruit and sugar boiled to a thick consistency.