Many authors use the terms "floor" and "ground" interchangeably. However, these two terms are not interchangeable. They refer to very distinct areas of walking surfaces.
Floor
The term "floor" refers to the walking surface inside of a room or building. It specifically refers to an interior walking surface, whether wood, tile, concrete, etc., of a manmade structure.
Ground
The term "ground" refers to the solid surface of the Earth outside of a building or structure where people can walk outdoors. This does, however, include manmade exterior pavements, walkways, streets, driveways, sidewalks, so long as they are outside of any building.
Though these terms both refer to walking surfaces, the distinguishing determination is location. Floor refers to an interior surface, while ground refers to an exterior surface, and these two terms are not interchangeable.