A ceiling system is an overhead interior surface that covers the upper limit of a room. It is not generally considered a structural element, but a finished surface concealing the underside of the floor or roof structure above.
Ceilings are classified according to their appearance or construction. A cathedral ceiling is any tall ceiling area similar to those in a churh.
A dropped ceiling is one in which the finished surface is constructed anywhere from a few inches or centimetres to several feet or a few metres below the structure above it. This may be done for aesthetic purposes, such as achieving a desirable ceiling height; or practical purposes such as providing a space for HVAC or PIPING. An inverse of this would be a RAISED FLOOR