Architraves are the surrounds that you see on the outside of a door frame, running from the skirting boards around the door and down again. The architrave is designed to cover any gaps between the door and the wall because there is usually a small gap, or rough edges on the plastering when the decoration has been completed.
Oak architraves are the choice of the modern luxury home whereas pine or mdf architraves are found in the vast majority of homes.