A ceiling is an overhead interior surface that bounds the upper limit of a room. It is generally not a structural element, but a finished surface concealing the underside of the floor or roof structure above.
A cathedral ceiling is any tall ceiling area similar to those in a church.
A dropped ceiling is one in which the finished surface is constructed anywhere from a few inches to several feet 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.
A concave or barrel shaped ceiling is curved or rounded, usually for visual or acoustical value, while a coffered ceiling is divided into a grid of recessed square or octagonal panels, also called a lacunar ceiling.
Ceilings have frequently been decorated with fresco painting, mosaic tiles and other surface treatments. While hard to execute (at least in situ) a decorated ceiling has the advantage that it is largely protected from damage by fingers and dust. In the past, however, this was more than compensated for by the damage from smoke from candles or a fireplace. Many historic buildings have celebrated ceilings, perhaps the most famous is the Sistine Chapel ceiling by Michelangelo.