What is the difference between wax and polish?

A wax is a protective coating, and a polish is an abrasive which removes dead paint --  think of it as liquid sandpaper. So you would polish a car to try to improve the paintwork, then apply a wax over the top to protect the paint.

However, there are exceptions to this rule as there are some combination products that do both jobs at the same time, such as Autoglym's Super Resin Polish, which is a light chemical polish, but also a protective wax.