Crown is the concrete at the top of a chimney. It seals off the air space between the outer walls of a masonry chimney and the flue liner. It slopes away from the liner and overhangs the chimney to shed water.
Splay or Wash is a mortar coating a-top a brick, block, stone or stucco chimney. A Wash keeps water from entering the chimney to prevent deterioration during the freeze thaw cycles. A Wash with cracks is the first point of water entry in any weather exposed chimney. Unlike a crown, a Wash is not concrete and does not overhang the edge of the chimney.
Smoke Shelf is the area at the bottom of the smoke chamber and is the back wall of the firebox. The shelf is located at the intersection of the smoke chamber and the firebox. Typically there is a damper on the forward side of the smoke shelf.
Ash Dump (Ash Pit) is an opening, usually with a hinge door and located at the bottom of the fireplace, where ashes can be dumped. Also , it can be the receptacle below the opening in which ashes collect before removal.
Chimney Cap is the protective covering or housing for the top of a chimney intended for preventing the entry of rain, snow, animals, birds, etc., and for preventing downdrafts. Chimney caps are also called flue caps or rain caps.