In thermal management, fans are classified as objects that forces air at a volumetric rate to cool certain devices, like a microprocessor.
There are numerous types of air moving products including axial, propeller, and tubeaxial fans. Other air movers consist of impellers and blowers (centrifugal & crossflow).
Fans, impellers, and blowers could be distinguished by their size, shape, but more importantly, the flow of air (measured in CFM) given the static air pressure.
A fan can basically have a high output of CFM, but at a lower level of air pressure, whereas blowers and impellers move smaller amounts of air at a greater level of pressure.
This paper from DAU Components explains how to make the right choice.