A showman's road locomotive or showman's engine is a steam-powered road-going 'locomotive' designed to provide power and transport for a travelling funfair or circus. Similar to other road-going traction engines, showman's engines were normally distinguished by the addition of a full-length canopy, a dynamo mounted in front of the chimney, and brightly coloured paintwork with ornate decorations. The dynamo was used to generate electricity to illuminate and power various fairground rides. Although originally the ride's motion was powered by an internal steam engine, some later rides were driven direct from the showman's engine via a belt drive.

A traction engine is a steam-powered tractor used to move heavy loads on roads, plough ground or to provide power at a chosen location. The name derives from the Latin tractus, meaning 'drawn', since the prime function of any traction engine is to draw a load behind it. They are sometimes called road locomotives to distinguish them from railway locomotives – that is, steam engines that run on rails.