An elaborate display mounted on a platform carried by a truck (or pulled by a truck) in a procession or parade WordNet 3.0 & Open English WordNet

A float is a decorated platform, either built on a vehicle like a truck or towed behind one, which is a component of many festive parades, such as those of Carnival in Rio de Janeiro, the Carnival in São Paulo, the Carnival of Viareggio, the Maltese Carnival, the Macy's Thanksgiving Day Parade, the Key West Fantasy Fest parade, the Mardi Gras in New Orleans, the 500 Festival Parade in Indianapolis, the United States Presidential Inaugural Parade, and the Tournament of Roses Parade. Wikipedia

A decorated vehicle or moving platform, could be animal- or man-drawn or motorized, used in a festive parade Wikipedia Disambiguation

An elaborately decorated trailer or vehicle, intended for display in a parade or pageant. Wiktionary

Trailer or vehicle decorated for a parade. Wiktionary (translation)