A butte is a hill with a flat top and steep sides, standing on its own. You see them in the dry west of the United States — the desert films are full of them. The top used to be part of a wider high area; the land around it wore away, and this harder piece stayed. A mesa is the same idea but bigger and wider; a butte is the smaller leftover. The word was borrowed from French butte, a mound, and further back it is related to English butt in an old “mound / blunt end” sense — though actually that is not the body-part word students think of first. It is a geography word, not city English.

平頂孤丘（美西地形用語；比 mesa「桌山」小）