Alien means belonging to a different country, race, or group, usually one you do not like or are frightened of.
You use alien to describe something that seems strange and perhapsfrightening, because it is not part of your normal experience.
If something is alien to you or to your normal feelings or behaviour, it is not the way you would normally feel or behave.
An alien is someone who is not a legal citizen of the country in which they live.
In science fiction, an alien is a creature from outer space.