First sexual intercourse after ending it with your significant other. Done primarily to reaffirm that you are still in the game and a one-time pass to engage in guilt-free, no-strings-attached indulgence of your primal desires with someone who would otherwise be socially off-limits.
"My old gal-pal Bobbie came over and banged my brains out last night. Don't think she's looking for a relationship though. She just broke up with her boyfriend. so it was probably her Free Agent Fuck."