A trolleybus is a bus that runs on electricity taken from wires hung above the road. Two poles on its roof reach up and touch the wires, and that is where the power comes from. It matters that a trolleybus has rubber tyres and runs on the ordinary road surface — that is what makes it a bus and not a tram. A tram runs on metal rails set into the street; a trolleybus is free to move to the kerb, pull round a parked car, and change lane a little, but it cannot leave the wires. You will see the word in writing about cities and transport, and in older photographs of European and East Asian cities. Taiwan does not have them, so it will not be a familiar sight to your students, but many cities still run them — they are quiet and produce no smoke on the street. Some people write it as two words, trolley bus, and it is also called a trolley coach; in older British speech, a trackless. In American English on its own, trolley usually means a streetcar on rails, which is a different vehicle again.

無軌電車（台灣少見，但陸港與歐洲城市常見；要跟有軌的「電車／路面電車」分開）。