The definition of "alien"

Im no scientist, but I would like to clarify that "alien" life arent just the green man-like creatures you find in movies, or the large evil bugs.

Even a microscopic lifeform in Mars can be considered "alien" since, by definition, it is a form of life outside of our world.

So those people "disappointed" in the Mars missions because there are no green men or giant bugs need to know that even those microscopic lifeforms can be called aliens.