A fork of Rural Dictionary
When you jack off for a really long time, and some of the cum that's will eventually burst out just sorta sits on the tip of your dick. Prebust is normally clear, not white.
Jack: Dude, I have sooooooo much prebust on my tip! John: Well you wouldn't if you weren't jacking off for so long! Jack: But it's the Animal Channel. It's the only porn I'm allowed to watch!