movement is a metal surface that all other components are connected to.
The main plate is the most basic element of any movement. It is typically machined to make room for the wheels, shafts, screws, and other elements of the movement. These components are usually anchored by bridges or cocks that are screwed to the main plate. Sometimes material is removed from the main plate to leave decorative gaps, a process known as skeletonization.
Some movements have multiple plates stacked together. For example the classic Glashütte three-quarters plate arrangement sandwiches most components between the main plate and a similar large piece that only exposes the balance through a 1/4 opening. When plates are used for construction, components are sometimes anchored using screwed chatons rather than directly into the plate itself.
Complicated movements may be constructed with multiple full plates to keep all the components in place. In this case, the plate nearest to the case back is known as the top plate, since this is the last plate put in place when the movement is assembled.