In the most simplest of simplest definitions, bun means sexual intercourse. It does not include oral sex though. Just your typical f*cking. Bun can also be combined with the word 'action' as in the example listed below.
Did you get any bun last nite from that slizzy?
Nah...we just fooled around a bit, but no bun action.
Nah...we just fooled around a bit, but no bun action.
by The Bonaire June 27, 2005