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A pied-à-terre is a small living unit typically located in a large city (typically an apartment or a condominium

Well, in French it translates literally to "foothold" or "foot on ground," but in usage it is simply a temporary or secondary place of lodging. So no, it doesn't have to be on the bottom floor. Feel free to lodge in the upper stories!

It's usually intended to be a sort of part-time home, either for weekends, or some other limited period of time.