Persons who dress and/or act like they are bums, yet have ipods, ipads or other expensive electronics.
iBums are frequently seen at "occupy" movement protests. Also most hipster students, and vagrant hippies in San Francisco and Santa Cruz
To take music off someone else's ipod without specifically selecting it.
"Wow, Joseph has alot of music on his ipod doesnt he?"
"Yeah, thats coz he ibummed my ipod!"