A motorcycle (also called a motorbike, bike, or cycle) is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions. Motorcycles are one of the most affordable forms of motorised transport in many parts of the world and, for most of the world's population, they are also the most common type of motor vehicle. There are around 200 million motorcycles (including mopeds, motor scooters, motorised bicycles, and other powered two and three-wheelers) in use worldwide, or about 33 motorcycles per 1000 people. This compares to around 590 million cars, or about 91 per 1000 people.
Around the world, motorcycles have historically been associated with subcultures. Some of these subcultures have been loose-knit social groups such as the cafe racers of 1950s Britain, and the Mods and Rockers of the 1960s. A few are believed to be criminal gangs. Books about motorcycle subcultures include Hunter S. Thompson's Hells Angels (1966), Lee Gutkind's Bike Fever (1974), and Daniel R. Wolf's The Rebels (1991).
Social motorcyclist organisations are popular and are sometimes organised geographically, focus on individual makes, or even specific models. Example motorcycle clubs include: American Motorcyclist Association, Harley Owners Group and BMW MOA. Some organisations hold large international motorcycle rallies in different parts of the world that are attended by many thousands of riders.
Whereas many social motorcycle organisations raise money for charities through organised events and rides, some other motorcycle organisations exist only for the direct benefit of others. Bikers Against Child Abuse (BACA) is one example. BACA assigns members to individual children to help them through difficult situations, or even stay with the child if the child is alone or frightened.
At the other end of the spectrum from the charitable organisations and the motorcycle rights activists are the "outlaw motorcycle gangs". These are defined by the Provincial Court of Manitoba as: "Any group of motorcycle enthusiasts who have voluntarily made a commitment to band together and abide by their organisations' rigorous rules enforced by violence, who engage in activities that bring them and their club into serious conflict with society and the law". The Federal Bureau of Investigation (FBI) and Criminal Intelligence Service Canada have designated four MCs as Outlaw Motorcycle Gangs (OMGs), which are the Pagans, Hells Angels, Outlaws MC, and Bandidos, known as the "Big Four".