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A fan is a device that moves air by rotating blades powered by an electric motor or other source. Its main purpose is to create airflow for cooling, ventilation, or air exchange. Compared with a blower, a fan typically generates lower pressure. The blades impart momentum to the surrounding air, producing a downstream flow and a low-pressure region behind the blades.

Fans are categorized by design and mounting. Axial fans have blades parallel to the rotation axis and move air along the axis; they are common in household ceiling, desk, and pedestal fans. Centrifugal (radial) fans use curved blades to discharge air perpendicular to the axis, delivering higher pressure for ventilation and exhaust. Other forms include box, tower, and inline duct fans used in HVAC and electronics cooling.

Applications include personal cooling, room ventilation, electronic and equipment cooling, and industrial ventilation. They are used in homes, offices, factories, and data centers, where efficiency, noise, and reliability matter. Safety features include guards to prevent contact with moving blades, and proper installation away from moisture or heat sources. Maintenance may involve cleaning blades, lubricating bearings, and checking electrical connections.

In addition to a mechanical device, the word fan also refers to a person who is an enthusiastic admirer or supporter of a person, team, or entertainment property. Fans often organize into communities called fandoms, participate in events, and share content online. The term is commonly used neutrally, though it can carry informal or slang connotations in some contexts.