Isolated means far away from everyone or everything else. The hermit who lives on a remote island is isolated from the rest of the world, with nothing but coconuts and fish to keep him company.
The word isolated comes from the Latin word insula, which means island. You don't have to be on a remote island to feel isolated, though. Even people who live in big cities can feel a sense of isolation if they don't have many friends and spend a lot of time alone. In addition to remote or set apart, isolated can mean a single event, or incident. The high school students assured their principal that the cafeteria food fight was an isolated incident, promising that it would never, ever happen again.