In watchmaking, the term "caliber" (or "calibre") refers to the specific model or design of a watch movement, which is the mechanism that drives the watch and powers its functions. The caliber is essentially the heart of the watch, comprising various components such as gears, springs, and escapements that work together to measure and display time. Each caliber is unique in its construction and can vary significantly in terms of complexity, size, and functionality.

Watch manufacturers often develop proprietary calibers, which are identified by specific numbers or names, to distinguish their movements from those of other brands. These calibers can be either mechanical, relying on a mainspring and gear train, or quartz, using electronic components and a battery. Mechanical calibers are further divided into manual and automatic, with the latter being self-winding through the motion of the wearer's wrist.

The design and craftsmanship of a caliber are crucial to a watch's performance, accuracy, and durability. High-end watchmakers often showcase their calibers through transparent case backs, allowing enthusiasts to appreciate the intricate engineering and aesthetic details. The development of a new caliber is a significant achievement in horology, reflecting innovation and expertise in watchmaking.