Rotor Saliency
Rotor saliency is a directional difference in a rotor's magnetic reluctance, created by unequal magnetic paths along different rotor axes.
How it produces torque
A salient rotor does not respond magnetically the same way in every direction. Projecting poles, flux barriers, magnet cavities, and steel bridges can all create that anisotropy. When the stator field is controlled at the appropriate angle, the rotor tends to align along its lower-reluctance path and produces reluctance torque.
Where it appears
Synchronous reluctance and switched reluctance motors depend on saliency as their principal torque mechanism, although their excitation and control differ. Interior permanent-magnet motors can combine magnet torque with reluctance torque because their embedded magnets and barriers also make the rotor salient. Surface-magnet rotors usually have less geometric saliency.
Greater saliency is not automatically better. Barrier shape, bridge strength, magnetic saturation, torque ripple, acoustic forces, high-speed stress, and control limits must be balanced. Saliency is a magnetic property of the rotor geometry, not physical imbalance or an off-center rotor.
For construction detail, see EV Motor Construction and Windings and the deeper explanation of Reluctance Motors.