Original: 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.
Simplified: A trolleybus (also known as trolley bus, trolley coach, trackless trolley, trackless tram or simply trolley) is a bus, which get its power for the electric engine from a pair of powerlines, which is above the street.