1. Any surface turned back from the face of a principal surface. 2. The ending of a small splash wall or a wainscot at right angle to the major wall. 3. The continuation of a molding or finish of any kind in a different direction. 4. In HVAC, a term for the return-air duct of a forced air heating/cooling system. 5. The continuation in a different direction of the face of a building or any member.