Floor? Ceiling?

Why do we call it a ceiling? Because it is above us, but even the room can be the floor. If I stand on te wall is it the floor. Is anything the floor if I am under it? The floorboard of my car is the undercarriage if I am under it. Even ceiling tiles could be floor tiles...? Does this mean that there are no actual ceilings, and that everything is a floor when we stand on it? Which means there are no limits.