In architecture, a cornice is generally any horizontal decorative moulding that crowns a building or furniture element—for example, the cornice over a door or window, around the top edge of a pedestal, or along the top of an interior wall. A simple cornice may be formed just with a crown, as in crown moulding atop an interior wall or above kitchen cabinets or a bookcase.
Illustrations of various examples of ancient Egyptian cornices, all of them having cavettos
Cornice of Maison Carrée (Nîmes, France), a Roman temple in the Corinthian order, with dentils nearest the wall.
A wide box cornice with lookouts
A close cornice
Moulding, or molding, also coving, is a strip of material with various profiles used to cover transitions between surfaces or for decoration. It is traditionally made from solid milled wood or plaster, but may be of plastic or reformed wood. In classical architecture and sculpture, the moulding is often carved in marble or other stones. In historic architecture, and some expensive modern buildings, it may be formed in place with plaster.
Decorative plaster mouldings and coving in a late Victorian town house in South Wales.
Moldings from 1728 Table of architecture in the Cyclopedia