Earthling is an alternate term to refer to a member of the Human race, particularly one born on their homeworld, Earth. It was apparently the favored term during the Ur-Quan Slave War. In all other contexts, including most Hierarchy communications of the Star Control II era, "Human" remained the most common term.
In addition to the Earthling Humans theres also the Unzervaultian Humans from the Vela part of the Vela-Zeeman star system. The humans from this regions were politically speaking distinct from the humans of the Sol system and there inner colonies near Sol. Basically in short Earthling is the names of both a civilization and a form of "Hyper-Nationalism" and the whole Earth-Moon system gets united and sometimes the Whole solar system such as the case in the Star Control universe.
Earthling has passed out of popular usage, except in the official designation for the Human combat vessel: the Earthling Cruiser.
See Also: Human