Things that are entertaining are enjoyable and distracting. Going to the circus is an entertaining way to spend an afternoon.
Activities like playing games and watching movies can be entertaining, and you can also describe a friend who's particularly funny or fun to be with as entertaining. The adjective comes from the related verb, entertain, which meant "keep up, maintain, or keep someone in a certain frame of mind" in the fifteenth century. It comes from the Old French entretenir, "hold together."