a widely used gramatically "incorrect" past form of swim. The correct past form of swim is swam, but it sounds stupid to say, so we usually say swum instead.
21patrick60: dude i wish we had swum at your grandparent's instead of playin gears all day & givin up on wave 19
bob: wait i hav an idea! lets hit eachother with lightsabers like mature 15 year olds!