Green’s Dictionary of Slang

jam n.1

[SE jam, a crush; 19C SE crush, a party]

1. [19C–1920s] (US) a social gathering or party; a crowd.

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

(a) [late 19C+] a problem, a difficult situation; usu. in a jam.

(b) [20C+] (US, also jamb) a disagreement or a fight.

(c) [1930s–50s] (US drugs) an overdose [‘it gets you in a jam’ (Spears, 1986)].

3. [1930s+] (US black) swing or other popular music.

4. [1950s+] (US black) a party with music.

5. [1950s+] music in general, a song, a record, a performance of jazz, rock or rap music (orig. with a dance routine).

6. [1970s+] (US gay) a spontaneous party that ends in an orgy or a big fight.

7. [1990s+] (W.I.) a crowd in a venue that is at full capacity.

In compounds

jambox (n.) [box n.1 (4b)/SE box]

[1980s+] (US campus) a portable stereo tape deck; latterly CD system.

In phrases

blind jam (n.) [fig. use of SE blind, i.e one cannot ‘see’ a charge]

[1930s] (US Und.) an arrest without a specific charge.