a homeless person who lives by asking for money or food

bums had been known to wander up to their door and ask for a sandwich

a person who devotes a great deal of time to a specified activity

a ski bum

get (something) by asking or begging

they tried to bum money off us

she bummed a cigarette from me

I bummed a ride into town with him

of poor quality; bad or wrong

not one bum note was played

a person's buttocks or anus

if you sit there you'll get a cold bum