US/Canada
1. Pejorative for a homeless person, - especially one that makes no attempt to work or better himself (contrasted with the more respected working homeless “hobos”). Probably comes from the expression “lazy bums.”
Get a job you F’ing bum.

2. To shamelessly ask for something (in the manner of a bum – see above).
Dude can I bum a cigarette, five dollars, and a ride to the…

3. A loser with nothing going for him (no job, no aspirations etc). Especially an unworthy husband or boyfriend.
I can’t believe she’s with Jim. Always drinking, never workin, the guy is a bum.

UK/Commonwealth:
4. The more polite way of saying ass.
Does my bum look big in this?

5. To do in the bum.
I bummed a tart.

Afganistan
6. Bum is a major city in Afganistan.

Someone who does nothing all day and expects everyone to bend over backwards to please them.

Someone who has no liscense, no car, no job, no girl.

To be anally invaded without consent.

Ass, butt, booty, gluteus maximus....

This is the name of someone that also goes by shrek. This person is bad at basketball .

Short-word for bummer. For use when something negative happens.

Anal sex. When a man inserts his cock into another mans ass and fucks him until he shoots his load up the mans ass.