What does it mean when a drive is "bus powered"?

What does it mean when a drive is "bus powered"?

Ali Nasri (Computer Specialist, Mac 911 Inc.) gives expert video advice on: How many USB ports should I look for in a new computer?; How many PCI Bus Slots should I look for when buying a tower? and more...

A bus powered drive is a drive that does not require a power supply. The cable that connects the bus powered drive to the computer provides power to the drive and that same cable provides data transfer.