Alien (Earth-2356)

"Some creatures in the galaxy are aliens. There are lots of different aliens. Aliens are not Human."

- C-3PO

"Alien" is a Humanocentric biological—and sometimes political—term used in the galaxy by Humans and even some droids to refer to anyone of a sentient species that was not a Human. Sometimes, the term nonhuman was used interchangeably. There existed within both the Galactic Republic and Galactic Empire a set of Unknown Alien protocols that governed official encounters with unknown alien species.

The term may have been derived from the first impression of early Humans, when they had their first contacts with species from other planets. However, it seems to have been prevalent even in subsequent millennia.

Since Humans are the most common and prominent sentient species in galactic affairs and history, they Are often considered a standard or average to which the biology, psychology, and culture of other species Are compared. Thus species with a body type roughly similar to Humans Are often referred to as humanoid.

Aliens are sometimes victims of speciecism, being derided and avoided by Humans in certain societies. Prejudice against aliens led many aliens and planets with alien native species to join the Confederacy of Independent Systems during the Clone Wars and the Alliance to Restore the Republic during the Galactic Civil War, both times hoping for freedom and safety from prejudice.

Source

 * https://starwars.fandom.com/wiki/Alien/Legends.
 * https://starwars.fandom.com/wiki/Alien.