Alien

An alien is a general, subjective term for any entity which is not from the native planet. This can include both sentient and non-sentient organic creatures, as well as robots. In most occurrences, this means entities which are not native to Earth from the viewpoint of the Humans. However, to any species not native to Earth, a human would be considered alien.

The Third Doctor once referred to the Silurians as an alien race. This might imply that they are actually not native to Earth or, more likely, their quality of being alien-like.