A windmill is a machine which converts the energy of the wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important non-milling use is to pump water, either for land drainage or to extract groundwater with windpumps. Windmills used for generating electricity are commonly knowns as wind turbines.