@Aqua And, aside from the dictionary, the way I defined it is how the words are most commonly used, which is almost more important. When someone uses ground inside it is odd, or I would go as far to say sounds wrong. It sounds like one of those things you get corrected on when you are a kid. Or, second language like my husband. Some people go as far as to be more specific about the flooring material: the tile, the carpet, the linoleum. Or, instead of the ground: the asphalt, the blacktop, the grass. Floor is short for flooring from what I would guess. However, if a cop yelled out, “hit the ground,” or anyone said it for that matter, I would not overthink it. That would be a special circumstance. It would make sense also that if that is a common expression used by police officers they might stick to the one phrase for easy understanding and it would be appropriate inside and out.