There are many systems for classifying types of motorcycles, describing how the motorcycles are put to use, or the designer's intent, or some combination of the two. Six main categories are widely recognized: cruiser, sport, touring, standard, dual-purpose, and dirt bike. Sometimes sport touring motorcycles are recognized as a seventh category. Strong lines are sometimes drawn between motorcycles and their smaller cousins, mopeds, scooters, and underbones, but other classification schemes include these as types of motorcycles.
There is no universal system for classifying all types of motorcycles. There are strict classification systems enforced by competitive motorcycle sport sanctioning bodies, or legal definitions of a motorcycle established by certain legal jurisdictions for motorcycle registration, emissions, road traffic safety rules or motorcyclist licensing. There are also informal classifications or nicknames used by manufacturers, riders, and the motorcycling media. Some experts do not recognize sub-types, like naked bike, that "purport to be classified" outside the six usual classes, because they fit within one of the main types and are recognizable only by cosmetic changes.
International Coordinating Committee of the Expert Group for Motorcycle Accident Investigations (2001), Motorcycles: Common International Methodology for On-Scene, In-Depth Accident Investigation, Paris: Road Transport Research Programme; of the Directorate for Science Technology and Industry; of the Organization for Economic Cooperation and Development, OECD/DSTI/RTR/RS9/ICC