I didn't want to write WTF on a comment board so instead I thought of abbreviating "what in god's great name", but before I wrote it I thought of looking it up and there wasn't an example. So I'm trying it here...

A jack off buddy (from 'cum' /'come', meaning 'semen', and 'companion'); a friend that you get together with for sessions of solo or mutual masturbation
Variant of: cumpanion (from 'companion' & 'cum'); jack off buddy & wank bud & JO buddy
Similar to: fuck buddy