Alien

Alien is an English term with several related meanings. In its most general sense, it refers to something that is foreign or belonging to another, derived from Latin alienus. In everyday use, it can describe people from a different country or culture who live in another place; in science fiction and public discourse, it often denotes a being from another world.

In science, alien commonly refers to extraterrestrial life or life forms from outside Earth. No confirmed evidence exists as of now. Scientists search for life by studying planets in habitable zones, analyzing atmospheres for biosignatures, and listening for signals through projects like SETI. The term embraces microbial life to technologically advanced civilizations. The Drake equation and Fermi paradox are used to frame questions about prevalence and detectability of alien civilizations.

Legal and administrative usage uses alien to mean a non-citizen or foreign resident. Terms vary by jurisdiction; many countries prefer "foreign national" or "non-citizen" in official language. Rights, duties, and pathways to residency or citizenship are determined by national law.

Cultural usage by media and popular culture has produced countless depictions of aliens, ranging from benevolent visitors to hostile invaders. These portrayals influence public perception and science communication but do not constitute evidence for or against the existence of extraterrestrial life.