无轨电车是一种通常由架空接触网供电、电动机驱动，不依赖固定轨道行驶的道路公共交通工具。而在有些国家或地区（如日本），无轨电车则属于轨道交通的范畴。正因无轨电车兼具道路汽车和轨道交通二者的优缺点，使得其成为当代备受争议的一种交通工具。

无轨电车的车身和底盘一般与普通巴士相同，但车顶需要安装一对受电杆，用于从接触网的一对触线受电并形成电流通路。一般地，无轨电车的受电杆脱线则会失去动力；而装备有动力蓄电池、超级电容器或柴油发电机的双动源无轨电车，则可在没有架空接触网的路段实现离线行驶。

A trolleybus (also known as trolley bus, trolley coach, trackless trolley, trackless tram [in early years] or trolley) is an electric bus that draws power from overhead wires (generally suspended from roadside posts) using spring-loaded trolley poles. Two wires and poles are required to complete the electrical circuit. This differs from a tram or streetcar, which normally uses the track as the return path, needing only one wire and one pole (or pantograph). They also are distinct from other kinds of electric buses, which usually rely on batteries. Power is most commonly supplied as 600-volt direct current, but there have been, and are, exceptions.