|a large motor vehicle, having a long body, equipped with seats or benches for passengers, usually operating as part of a scheduled service; omnibus.|
The term bus has been around since the early 19th century but the bus as we know it today has been around since the conception of the automobile in the early 20th century. Busses are extremely efficient at transporting passengers along routes that can change frequently or are of lower density where traffic moves smoothly. Since a bus typically operates in mixed traffic it is subject to the same guidelines forced on automobiles.
Bus rapid transit is an alteration of a typical bus transit system where some or all of the line is operated on a dedicated roadway alongside mixed traffic. Such systems are much more cost effective to implement and maintain but do not offer the density mindset that rail transit offers.