To figure out your chances of having sex with your partner or on the first date.

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

Sport or recreation

When one Sings and Humms at the same time! It is quite a pleasant sound a bit like a young walrus' mating call!