basically someone who's ass you would slap in the boys locker room or someone who's ass you want to grab and squeeze ;)
"lets go catch a flick later chum"
"will you be my chum?"
2.Shark bait composed of unwanted or useless fish parts. chummed; chummer; chumming; ect.
3.SLANG.Semen or sebum see also "smegma".
adj."They are acting chummy"
2."I saw a chummer chumming with chum, he chummed all day"
3."Suck my chum!"
"Goddamn my chum is rashy... I hope I didn't catch anything."
"That fudgepacker tried to grab my chum in the showers after the game! What an asshole!"