An alien is a being that is not from one's own homeworld.
Lost in Space[]
The Robinson family encountered many aliens after the Jupiter 2 launched from Earth.
Land of the Giants[]
When the "Spindrift" crashed on an unknown planet the humans discovered people who were twelve times their size, who they often called "the Giants". ("The Crash") Many of the Giants wanted to capture the humans, or "little people", because their government would give them a large reward.