Green’s Dictionary of Slang

1. (US) a social gathering or party; a crowd.

1812		‘The Theatre’ in H. Smith Rejected Addresses 105: All is bustle, squeeze, row, jabbering, and jam.
1827		Longfellow in Longfellow Life of H.W. Longfellow I (2003) 123: I have been several times to her evening jams; but, as it was Lent, there was no dancing .
1841		F. Jackson Victim of Chancery 57: It is not our intention to give a detailed description of all the etiquette, or all the vulgarity, that is found at the ‘jam’ of a city Nabob.
1851		Chicago Daily Journal 19 Feb. 3/1: Party succeeds to party, from a quiet little ‘social’ to the pretending and fashionable ‘Jam,’ where ‘wheeling about and turning about’ is the order of the evening [DA].
1857		D.P. Thompson Trappers of Umbagog 3: One of those social gatherings that have been sometimes [...] not inaptly denominated a jam.
1880		R. Grant Confessions of Frivolous Girl 41: A nearly solid jam of girls, clustered together in chairs.
1885		Bulletin (Sydney) 24 Jan. 6/3: Then, in return for Graham’s ‘jam,’ friend Ballington expressed a ‘fervent wish for the future happiness and prosperity of the Chief Secretary,’ and the Harmy fired a volley of Amens.
1920		F.S. Fitzgerald ‘May Day’ in Bodley Head Scott Fitzgerald V (1963) 181: People [...] Whole jam of them.

2. in fig. uses, i.e. that which crushes.

3. (US black) swing or other popular music.

1937		in Kalmar & Ruby Life of the Party [film script] Who brought the jam to old Jamaica / Who made them swing in Singapore? [HDAS].
1938		D. Burley N.Y. Amsterdam News 29 Jan. 19/1: Yank in your top-piece, neighbor mine, and tun[e]-in on the ‘jam’.
1944		‘Jiver’s Bible’ in D. Burley Orig. Hbk of Harlem Jive.
1952		(con. 1948) G. Mandel Flee the Angry Strangers 456: Let’s go up Tenth Street, Normie; they got some Sunday jam at Nelson’s. Let’s do listen to some good ole music. Some good Dixie.
1957		H. Simmons Corner Boy 36: Dig this crazy jam.
1978		R. Price Ladies’ Man (1985) 156: What a dynamite jam. I slipped it on the box. Just one record.

4. (US black) a party with music.

1950		New Yorker 4 Feb. 34: I got into a jam attending a jam – one of those phonograph-record jams, or platter parties, to which each guest brings his or her favorite hot or blues recording.
1969		Current Sl. III:3 8: Jam, n. A dance.
1971		H.E. Roberts Third Ear n.p.: jam n. dance or party.
1987		Newcleus ‘Huxtable House Party’ 🎵 We’re throwing a jam that you don’t want to miss.
1995		L. Stavsky et al. A2Z.
2000		W. Shaw Westsiders 48: That’s when the block parties and the park jams that incubated hip-hop started.

5. music in general, a song, a record, a performance of jazz, rock or rap music (orig. with a dance routine).

1957		H. Simmons Corner Boy 37: What’s the name of the jam? [record].
1965		B. Jackson Get Your Ass in the Water (1974) 206: The cats put on a platter by Miles and Bird, / the terriblest jam I ever heard.
1976		R. Price Blood Brothers 159: They would throw on some heavy jams, some Curtis, some James Brown [...] you name it!
1981		M. Baker Nam (1982) 26: I liked listening to her. She put on some good jams.
1988		Ice-T ‘Power’ 🎵 That adds up to six years of makin’ ok jams.
1993		K. Scott Monster (1994) 275: ‘Remember that Temprees song [...] “We’ve Only Just Begun”’ [...] ‘Yeah, that’s a bad jam.’.
1993		Lerner et al. Dict. of Today’s Words 97: Jam – the noise level of a party or event, as in, ‘Let’s pump up the jam here’.
1999		‘Master Pimp’ Pimp’s Rap 7: I slipped the DJ five dollars to play the number one slow jam for us.
2001		Eble Campus Sl. Fall 6: Jams – music.
2007		D.S. Mitchell Killer Tune (2008) 25: No jam is a success until the crowd closes its eyes and feels the things it cannot see.
2012		J. Díaz This Is How You Lose Her 95: You remember that José Chinga jam ‘Fly Tetas’?
2015		Guardian G2 3 July 13/1: Some of the slower sex-centred jams are a bit suspect.

6. (US gay) a spontaneous party that ends in an orgy or a big fight.

1972

B. Rodgers Queens’ Vernacular 117: jam [...] 2. a spontaneous party often ending in a spirited orgy or free-for-all with fighting, etc.

7. (W.I.) a crowd in a venue that is at full capacity.

1995

Francis-Jackson Official Dancehall Dict. 28: Jam capacity crowd: u. de dance last nite did jam, iah.