A trolley is a vehicle that carries many people and is powered by overhead electrical cables. You can also call a trolley a "tram," "cable car," or "streetcar."
If you've ridden a streetcar up and down the hills of San Francisco, you know what a trolley is. Trolleys often travel on rails that are built into the street, using electricity that comes from a third rail or overhead lines. Anyone who grew up watching "Mister Rogers' Neighborhood" on TV will remember the model Neighborhood Trolley that carried viewers into the Neighborhood of Make-Believe.