Crown Molding

The decorative piece of material that joins a wall and ceiling with a more pleasing set of cuts, bevels, angles and curves than the typical 90º joint. Alternate accepted spelling "moulding." Commonly used materials include wood, plastic, plaster, and resin.

An example of one profile, shown on an outside corner:

http://www.easycrownmolding.com/easy-crown-molding-gallery/crown-molding-design-ideas/