What is a pad saw?

This is another name for what most people call a 'Keyhole saw' . This has a blade of 6-8 inches, narrowing to a point, with fairly small teeth about 10-12 to an inch. The idea is to drill a hole in the wood or drywall, insert the saw and cut the hole you want. Many electricians and 'cable guys' use it to fit new boxes in existing walls.