A mountain bike is a bicycle designed for riding off-road, either on dirt trails or other non-pavement type environments.
While cyclo-cross bikes already existed, the earliest ancestors of modern mountain bikes were based around frames from road cruisers such as those made by Schwinn. Gary Fisher is normally credited with introducing the first purpose-built mountain bike in 1979.
Mountain bikes have fat, knobby tires for extra traction, and are usually fitted with shock absorbers on the front fork. Sometimes rear suspension is included as well. Mountain bikes are also often fitted with bar ends on the handlebars.
In French a mountain bike is called a VTT (vélo toute-terraine: "all-terrain bicycle").