Trolleybus

A trolleybus (also known as trolley bus, trolley coach, trackless trolley, trackless tram or trolley) is an electric bus that draws its electricity from overhead wires (generally suspended from roadside posts) using spring-loaded trolley poles. Two wires and poles are required to complete the electrical circuit. This differs from a tram or streetcar, which normally uses the track as the return part of the electrical path and therefore needs only one wire and one pole (or pantograph). They also are distinct from other kinds of electric buses, which usually rely on batteries. [Trolleybus. Wikipedia]