What is a hole saw.

A hole saw is a device that fits on a drill, (see image) that comes in various sizes to drill holes in wood studs. Electricians use them to run wires and plumbers use them to run pipes. Cheers, Tom

Tom gave you what you need but there are lighter, cheaper versions for light weight materials. What are you working on?

They are also used by carpenters to make holes in door for passage/lock set.

Chuck