This is any hardware on a door used to enhance appearance or functionality such handles, hinges or letter boxes.
This covers what is used on things like front and back doors or patio doors. The door furniture for external use often combines elements of safety as well decoration features such as names and numbers to indicate what your address is.
Internal door furniture can mean anything from hinges to door knobs. All add style to a home and is purely down to the individual what style is used.