As the name suggests, these are bikes specialized for closed-course, motocross competition.
They are all very high performance (and high-maintenance!), have stiff suspension meant for handling large jumps and “attacking” the terrain of a track. Their engines, transmissions and fuel capacity are best suited for motocross: explosive power, light-weight and shorter shift-ratios.
While they can be ridden on trails, they are not as well suited to woods-riding conditions as recreational or trail / enduro bikes. You will absolutely see Motocross bikes out on the trail for a wide variety of reasons. (Personal preference, dual-purpose to ride on Track and Trail, etc.) But in general, they are just not as well suited to trail/woods riding unless you are a very aggressive rider or racer. If you don’t believe us, try riding a Motocross Bike and then jump on an equivalent Trail Bike on a gnarly, rocky piece of single track and the contrast will be self-evident.
Last but certainly not least, being closed-course competition type bikes, they rarely (if ever) come with spark arrestors and exhaust systems that meet our strict 92db sound limit.
Examples of models in this category: Kawasaki KX-F, Yamaha YZ-F, Suzuki RMZ, KTM SX-F and Husqvarna FC series.