1. To wait for an event that will never occur. "The system is hanging because it can't read from the crashed drive". See wedged, hung.
2. To wait for some event to occur; to hang around until something happens. "The program displays a menu and then hangs until you type a character." Compare block.
3. To attach a peripheral device, especially in the construction "hang off": "We're going to hang another tape drive off the file server." Implies a device attached with cables, rather than something that is strictly inside the machine's chassis.