The Hall effect refers to the potential difference (Hall voltage) on opposite sides of a thin sheet of conducting or semiconducting material in the form of a 'Hall bar' (or a van der Pauw element) through which an electric current is flowing, created by a magnetic field applied perpendicular to the Hall element. Edwin Hall discovered this effect in 1879.
The ratio of the voltage created to the amount of current is known as the Hall coefficient and is a characteristic of the material that the element is composed of.
Hall effect devices are digital On/Off sensors constructed of semiconductor material used to sense the presence of magnetic fields. In brushless servomotors, they are used as position feedback when six-step commutation is employed.