A backlog occurs when a man, for reasons sometimes unknown, hasn't ejaculated in a long period of time. After this dry spell ,when the man ejaculates what emerges is reffered to as the backlog. This backlog is usually a massive amount of abnormally thick jelly-like cum that has been stored by his testicles over this period of time, and if not handled correctly can cause a massive mess. Backlog frequently occurs in men that are in relationships becuase they are so caught up by their girlfriend that they forget to regularly service themselves.
Guy 1: Hey man, I finally broke my dry spell after I broke up with Julie last night.
Guy2: Wow really? What was the damage?
Guy 1: Nothing much, just a serious amount of backlog and a serious mess afterwards.