The exact number of different motorcycle types varies depending on what you consider a "type of motorcycle." The biggest categories are standards, cruisers, sport bikes, touring motorcycles, and off-road or dirt bikes. Some people classify scooters as motorcycles. There are also several hybrid motorcycle categories like sport touring bikes that many consider a type of motorcycle in their own right.
Motorcycle categories are based on rider position, seat height, fairing, weight, engine size/power, suspension, and storage.