A wind turbine is a machine for converting the mechanical energy in wind into electrical energy. If the mechanical energy is used directly by machinery, such as a pump or grinding stones, the machine is usually called a windmill. If the mechanical energy is then converted to electricity, the machine is called a wind generator.

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A windmill is an engine powered by the energy of wind to mill grain, often contained in a large building as in traditional post mills, smock mills and tower mills. It also refers to small tower mounted wind engines used to pump water on farms. The modern wind power machines used for generating electricity are more properly called wind turbines.