A horse-bus or horse-drawn omnibus was a large, enclosed, and sprung horse-drawn vehicle used for passenger transport before the introduction of motor vehicles. It was widely used in the 19th century in the United States, Europe, and other nations where horse-drawn transport was used and was one of the most common means of public transportation in cities. In a typical arrangement, two wooden benches along the sides of the passenger cabin held sitting passengers facing each other. The driver sat on a separate, front-facing bench, typically in an elevated position outside the passengers' enclosed cabin. In the main age of horse buses, many of them were double-decker buses. On the upper deck, which was uncovered, the longitudinal benches were arranged back to back.

Similar, if smaller, vehicles were often maintained at country houses (and by some hotels and railway companies) to convey servants and luggage to and from railway stations. Especially popular around 1870–1900, these vehicles were known as 'private omnibuses' or 'station buses'. Coachman-driven, they would usually accommodate four to six passengers inside, with room for luggage (and sometimes additional seating) on the roof.

A small open wagon with or without a top, but with an arrangement of the seats similar to horse-drawn omnibuses, was called a wagonette.

Bus is a clipped form of the Latin word omnibus. A legend, promoted by the French Transportations Museum website, says the name is derived from a hatter's shop of the Omnes family in front of the first station opened in Nantes by Stanislas Baudry [fr] in 1823. "Omnes Omnibus" was a pun on the Latin-sounding name of that hatter Omnès: omnes (nominative plural) meaning "all" and omnibus (dative plural) meaning "for all" in Latin. Thence, the legend concludes, Nantes citizens gave the nickname of Omnibus to the vehicle.

Though it is undisputed that the term arose with Stanislas Baudry's company, there is no record of any Omnès hatter living in that street. In 1892, the son of Baudry's bookkeeper wrote in the Bulletin de la Société archéologique de Nantes that omnibus had a simpler origin. Baudry used to call his horsecars Dames blanches (White ladies), a name which, critics told him, made no sense. He then replied, with the Latin word: "Then, these are omnibus cars!" (cars for all). The name caught on immediately. Other stories about the name origin quickly spread out.

The term 'omnibus' carried over to motor vehicles. The 1914 book Motor Body-building in all its Branches, by Christopher William Terry, described an omnibus as having longitudinal seats with either a rear door or side doors.

The first known public transport service was the carrosses à cinq sols service launched by Blaise Pascal in 1662 in Paris. It was quite popular until fares were increased and access to the service for commoners was restricted. Services ceased after 15 years.

In Britain, John Greenwood opened the first bus line in Britain in Manchester in 1824. His pioneering idea was to offer a service where, unlike with a stagecoach, no prior booking was necessary and the driver would pick up or set down passengers anywhere on request. The first omnibus was introduced in London in 1831, and in 1838 legislation was passed to regulate them, requiring the drivers and conductors to obtain a license and wear a badge with the licence number on it.