Skeleton – a watch with a mechanism cut away to the minimum material by sawing and milling.  Skeleton mechanisms are often provided with fine engravings and chasings.  Built in between the transparent dial and glass bottom they create attractive, decorative watches.

Tourbillon – device invented by A. L. Breguet in 1801 to eliminate errors of rate in the vertical positions.  It consists of a rotating carriage or cage carrying all the parts of the escapement and the balance wheel.  This ingenious mechanism corrects the small gravitational error that exists in regular watches.

Complication – a watch with more than one function (e.g. alarm, moonphase, perpetual calendar, power reserve indicator, split seconds, repeater).  The term is usually used only for mechanical watches.

Grande Complication – a masterpiece of micro engineering.  It usually includes the maximum number of functions.  Displays hours, seconds, elapsed time, phases of the moon, and includes a split-second chronograph.  Can have 9 hands, over 950 parts, and automatic mechanical perpetual calendar programmed for 514 years.