Aliens are extraterrestrial life that does not originate from Earth. These as yet hypothetical forms of life range from simple bacteria-like organisms to beings far more complex than humans. The possibility that viruses might exist extraterrestrially has also been proposed.
In Tasty Planet two aliens appear talking in a Cutscene before their Galaxy is eaten by Grey Goo. However, they can't be eaten in the actual game.
They speak English, even though Aliens from another Galaxy most likely would have their own language. (This is probably done so the player can understand them).
Considering their vehicles, they are more advanced than humans.