All trolley cars are streetcars, but not all streetcars are trolley cars. The mule car and the horse car predated the mechanical systems, which came in several forms.
The cable car came along in 1877, when Andrew Halliday conquered the Clay Street Hill in San Francisco. And Thomas Edison experimented with battery-powered street cars (fueled by banks of batteries installed beneath the seats), which ran in several North Carolina cities. But the electric trolley — which drew its current from an overhead wire — soon outclassed and outgunned these systems, quickly dominating urban travel.
What made a trolley car a trolley car was the long, spring-loaded pole on the roof that connected it to the power lines overhead. At the upper end of the pole was a small wheel, which pressed against the wire and brought the current down to the motors below the car (the earliest trollies used a small, cartlike structure and a wire, instead of a wheel and a pole). When the power was applied to the motors, these rudimentary trolley cars moved forward, dragging the small “cart” along with them, in a “trolling” motion — hence the word “trolley.” The pole/wheel arrangement soon replaced the “cart,” but the name stuck.
The vehicles operated today in many tourist locations may be called “trolleys” by their operators, but they are no more than buses in drag — prettied up to look like old-time trolley cars, but about as far from the real thing as you can get without being accused of outright fraud.