Whats a “movement”?
A movement is the mechanism that actually calculates the passage of time–the “guts” of the watch, if you will. Like the engine and transmission of a car, watch movements are so fundamental to the quality of the watch that they are often manufactured by separate companies, or by the same company in a different factory. The movement is also the part of the watch which is usually covered by a warranty–much like the “engine and drivetrain” warranties that come with new cars.