Green’s Dictionary of Slang

rapping n.2

[rap v.1 (1e)]

(orig. US black) talking.

[US]R.R. Lingeman Drugs from A to Z (1970) 219: rapping [...] (1) talking. (2) random free-form conversation.
[US]A. Young Snakes (1971) 106: ‘We might have to talk to those people.’ [...] ‘I aint about to waste my good high rappin with them stuck-up cute niggers.’.