A transformer is an electrical device that changes the voltage of alternating current (AC) in a circuit. It consists of two coils of wire, known as the primary and secondary windings, wrapped around a core. When AC flows through the primary winding, it creates a magnetic field that induces a voltage in the secondary winding, allowing for either an increase or decrease in voltage. Transformers are essential in power distribution systems, enabling electricity to be transmitted over long distances efficiently. They help maintain safe voltage levels for homes and businesses, ensuring that devices can operate correctly without damage from high voltage.