Watch winding refers to the process of keeping an automatic (self-winding) watch powered and running accurately by maintaining tension in its mainspring when the watch is not being worn. Automatic watches have a rotor inside that spins with the natural movement of the wearer’s wrist, winding the mainspring and thus powering the watch. When the watch is not worn for an extended period, the mainspring's stored energy depletes, causing the watch to stop.

A watch winder is a device designed to simulate the natural wrist movements by rotating the watch gently in a controlled manner. This keeps the mainspring wound, maintaining the watch’s time, date, and other functions without the need for manual winding. Watch winders typically allow adjustment of the number of rotations per day (turns per day, TPD) and the direction of rotation (uni-directional or bi-directional) to match the specific winding requirements of different watch movements.

Watch winders are especially useful for collectors who own multiple automatic watches and do not wear each one regularly. They prevent the inconvenience of resetting the watch and help keep the lubricants inside the movement evenly distributed, potentially extending the watch’s lifespan. However, they are not necessary if you wear your automatic watch daily. Manual-wind watches and quartz watches do not benefit from watch winders, as manual watches require manual winding and quartz watches are battery-powered.

In summary, watch winding is the act of keeping an automatic watch’s mainspring tensioned, either by wrist movement or by a watch winder device, to ensure continuous operation and accuracy when the watch is not worn.