Green’s Dictionary of Slang

jam n.3

[jam tart n. (2)]
[late 19C+]

1. an attractive woman.

2. sexual activity, incl. intercourse, with a woman.

3. (later use US black) the vagina.

In phrases

bit of jam (n.)

1. [late 19C] the vagina; thus have a bit of jam, to have sexual intercourse.

2. [late 19C–1900s] an attractive woman.

elderly jam (n.) [‘Elderly jam is – elderly jam, and heaven preserve it, for man turns from it’ (Ware)]

[late 19C] an old woman.

lawful jam (n.)

[late 19C–1900s] one’s wife.

no-beyond jammer (n.)

[late 19C–1900s] an extremely attractive woman.