Cornice
A cornice is a moulding that covers the junction between a wall and a ceiling internally, or the projecting crowning element at the top of an external wall.
Internally, the cornice conceals the joint where wall and ceiling linings meet, which is a junction that would otherwise crack as the building moves. Profiles range from ornate plaster in period homes to a simple cove, or to no cornice at all.
Contemporary work often deletes the cornice in favour of a square-set junction, where the wall meets the ceiling in a clean line, or a shadow line, where a deliberate recess separates the two planes. Both look sharper but demand more accurate setting out and are less forgiving of movement.
Externally, a cornice is the projecting moulding that crowns a wall or sits beneath the eaves. It throws water clear of the wall below, which is why it appears on traditional masonry buildings.