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1.
A women that has engaged in anal sex. The term is considered derogatory by women that do not engage in anal sex, but a matter of pride for women that do. Often refers to women that are overweight or not highly attractive that perform anal sex as a means of competing with their prettier counterparts that will not engage in anal sex. Also can denote a women who saves her "virginity" by engaging in anal sex instead of vaginal sex.
Bumgirl: I gave my boyfriend my ass last night.
Non-bumgirl: Eww! You are such a skank. I guess that means you are a bum girl. Didn't it hurt?
Bumgirl: No, and he loved every minute of it.

Dave: Check out that girl over their with the big ass.
Raj: I bet she is a bum girl for sure.

Alvin: My girlfriend won't let me fuck her proper, she only wants to give me her ass until we are married.
Joe: What a total bum girl! At least you are getting something.

Maria: Was that guy you met at the bar last night good in bed?
Eve: No, he kept trying to play with my ass. He must have thought I was some kind of bum girl, but there is no way I am going to do that.
by Rex Roddy December 19, 2009