Green’s Dictionary of Slang

(US gay) genital-to-genital frottage.

1993

(con. 1950s) Kennedy & Davies Boots of Leather (2014) 199: The predominant form of [woman-to-woman] lovemaking [...] was what the clinicians called ‘tribadism’ or what most narrators for theis period call ‘friction’. Another narrator rembers women form this period calling it ‘banging’.