An escutcheon is a general term for a decorative plate used to conceal a functioning, non-architectural item. Escutcheons are most often used in conjunction with mechanical, electrical, and plumbing components and fixtures where a pipe, tube, or conduit passes through a wall [or other material] surface. The escutcheon is used to bridge the gap between the outside diameter of the pipe and the inside diameter of the opening in said surface.
Escutcheon can also refer to an item of door furniture. In this case, it is an architectural item that surrounds a keyhole or lock cylinder. Escutcheons help to protect a lock cylinder from drilling or snapping, and the surrounding area from wear it also prevents any bugs or dust getting into the house/room.