In E.T. the Extra-Terrestrial, the alien is called E.T.
The name is short for “extraterrestrial,” the generic term used for a being from beyond Earth. In the film, the stranded visitor has no ordinary human name. Ten-year-old Elliott discovers him hiding near his home and gives him the nickname E.T., which becomes the character's familiar identity for the audience and the other characters.
E.T. is a gentle alien explorer whose species visits Earth to collect plant specimens. He is accidentally left behind when government agents arrive, and Elliott, his brother Michael, and his sister Gertie hide him while trying to help him contact his people. E.T. demonstrates telekinesis, healing abilities, and a powerful emotional connection with Elliott.
The title character is sometimes described in expanded fictional material as an Asogian from the planet Brodo Asogi, but those details are not needed for the film's straightforward answer. Stitch is from Lilo & Stitch, Alf is a different television character, and Gizmo is the creature from Gremlins.