vehicle operated on the streets on rubber tires and powered by electricity drawn from two overhead wires by trolley poles. It is distinct from a trolley car, which runs on rails rather than on tires and is thus a form of streetcar.

In the late 1880s a number of small transit systems were put into operation using electric power supplied by the system of Leo Daft, of the United States, which used two overhead wires; electrical power was gathered by a small carriage, or troller, running on the wires. The troller was carried on the vehicle by a bent piece called a bow or by a collapsible and adjustable frame called a pantograph. The word trolley came from the little troller of Daft's system. Trolleybuses had the advantages of electric propulsion (more quiet operation, avoidance of fumes, and faster acceleration) and could load passengers at the curb, but they were less flexible than the motor bus.

A number of trolley installations were made in England, particularly London, and in the United States, but they were quickly replaced by buses. Trolleybuses were widely adopted by state-run urban transport systems in the Soviet Union, however, either alone or in conjunction with subways, streetcars, or buses. Other countries of eastern Europe adopted them, as did China, Switzerland, and Italy. By the late 20th century trolleybuses were still a major form of mass transit in many Russian cities, but the trend in most other countries was to replace them with buses.