What is alien definition?

An alien refers to a being from another planet or galaxy. It is a term commonly used to describe extraterrestrial life from other worlds. Aliens may be portrayed as intelligent, advanced, and capable of travelling across the universe. The concept of alien life has been a topic of discussion in science fiction literature and movies for many years. While many people believe in the existence of extraterrestrial life, there is yet to be any concrete evidence of such beings.