I have heard that stone trim at the top of a parapet wall sometimes referred to as a coping and sometimes as a cap. Are both these terms interchangeable?
The Brick Industry Association (BIA) Technical Note 36A titled "Brick Masonry Details--Caps and Copings, Corbels and Racking" states that the definitions of these terms vary by the dictionary or glossary used. For the purpose of the BIA Technical Notes, the covering at the top of a parapet is referred to as a coping. The term cap is used to refer to covers over projections that are within the wall. Caps may be the top stones of belt courses or stones covering an offset or change in thickness in masonry walls that are used for architectural effects.