The proper electrical term is "bridge rectifier." It consists of 4- diodes (electrical one-way check valves). The bridge rectifier's purpose is to change alternating current (AC) into direct current (DC) by eliminating one-half of the alternating current's sine wave.

During one-cycle of AC current there is a 1- positive and and 1- negative half-wave of equal amplitude of power, the bridge rectifier stops one of the half-waves amplitude from traveling along the circuit's path; when the cycle changes polarization current is allowed to flow in the opposite direction. The diodes are used in a series-parallel circuit arrangement in pairs.

These are what we call "voltage regulators" on small air-cooled engines. --Eds Small Engines