<span class="SFPTagline"> From SCIFIPEDIA </span>

A Terran is a human native (born on) inhabitant of Terra, the planet Earth. A Terran is a subset of the term Earthling, which is broader in interpretation in that it includes any species that originated on Earth.

The distinction is that if humans ever colonize mars, the distinction between Earthling and Terran becomes more obvious. For instance: First generation colonists, the people arriving will be Terrans and Earthlings. But the second generation, the children born on Mars will still be Earthlings, but they will not be Terrans - they will be Martians (a native inhabitant of Mars).