A skeleton clock is any clock or wristwatch, though typically mechanical in nature, in which the parts that usually conceal the inner workings of the mechanism have been removed or significantly modified so as to display these inner parts.
It is considered to be a showcase design and intentionally exposes to plain view the various gears, wheels and springs within the movement itself. There is no official definition of a skeleton clock per se, but a major portion of the main parts of the timepiece should be openly visible from the front of the clock and most often from the back as well in order for it to be considered and accepted as a skeleton clock. The parts most commonly showcased by a skeleton design are those exhibiting either the most movement or the most attractive design. These may include, but are not limited to the escapement, balance wheel and balance spring, mainspring, and tourbillon. Generally there is either no dial present in a skeleton clock, the dial is clear, or it has been limited to a ring around the edge of the case to provide a mounting surface for the hour markers. In the case of skeleton wristwatches, the back will usually be made of sapphire crystal or another clear material that affords easy examination of the parts protected within both from the front and from behind.