Exterior Door
The object in this picture is an exterior door. This is used as a portal between inside and outside of buildings, houses, or other constructions. This can be found at any building on the floor level.
Interior Door
The object shown in this classy selfie is an interior door. These are used either to allow, or disallow access between rooms in a house. Without doors, there would simply be an open passageway to travel through, and no one would have any choice of privacy. These are also useful in maintaining the ventilation and temperature in a house. This interior door was found in my house.