To bum: to mooch, to cadge, to supplicate, to beg. To ask in an ingratiating manner for charity.

As in the song

Halleluiah I'm a bum
halleluiah bum again
halleluiah give us a handout to revive us again
I went to a house
and knocked on the door
the lady said bum-bum you've been here before
halleluiah I'm a bum
halleluiah bum again
halleluiah give us a handout to revive us again.