The connexion of sections of an electrical circuit to a common conductor, called the ground, which serves as the reference for the other voltages in the circuit. The ground conductor on installed circuit boards is usually connected to the chassis, or metal frame, holding the electronic parts; the chassis is in turn usually connected to the third (round) prong on the power plug, which connects to a ground circuit that is, in fact,connected to the earth. This is important to avoid creating a shock hazard.