Molding is a strip of material with various cross sections used to cover transitions between surfaces or for decoration. It is traditionally made from solid milled wood or plaster but may be made from plastic or reformed wood.

A “sprung” molding is a strip that has beveled edges, allowing it to be mounted at an angle between two non-parallel planes (such as between a wall and a ceiling). Other types of molding are referred to as “plain”.

Types

There are a variety of common moldings:
Astragal - attached to one of a pair of doors to serve as a stop for the other door. The two types are “T-Astragal” and “Flat Astragal”. The later is primarily used for decorative purposes.
Base molding - used at the junction of an interior wall and floor to protect the wall from impacts.
Batten - a symmetrical molding that is placed across a joint where two parallel panels or boards meet.
Bed molding - a narrow molding used at the junction of a wall and ceiling. Bed moldings can be either sprung or plain.
Casing - the trim for both sides of a window opening.
Chair rails - a horizontal molding placed part way up a wall to protect the surface from chairs. Primarily used now for decoration.
Corner guard - a molding used to protect the edge of the wall at an outside corner, or to cover a joint on an inside corner.
Cove molding - a concave-profile molding that is used at the junction of an interior wall and ceiling.
Crown molding - a wide, sprung molding that is used at the junction of an interior wall and ceiling.
Drip cap - this is placed over a door or window opening to prevent water from flowing under the siding or across the glass.
Keel molding - with a sharp edge, resembling in cross-section the keel of a ship.
Screen molding - this is a small molding that is used to hide the area were a screen is attached to the frame.