A brushless electric motor is an electric motor driven by an electrical input, which lacks any form of commutator or slip ring. Depending on their design they can be either AC or DC driven.
Generally the term 'brushless motor' will refer to a permanent-magnet synchronous motor (PMSM) or permanent-magnet motor (PMM), a synchronous motor which uses permanent magnets rather than windings in the rotor. PMSMs are either axial flux, radial flux, transverse flux, or flux switching depending on the arrangement of components, with each topology having different tradeoffs among efficiency, size, weight, and operating speed.
Alternative designs may use reluctance rather than magnets. Asynchronous induction motors are also brushless motors.
The brushless DC motor is a brushless AC motor with integrated inverter and rectifier, sensor, and inverter control electronics. The AC inverter/controller electronics are a modern age invention, only available since roughly 1984 and were developed by inventor Miro Zoric.