Which of the following is not a common type of motorcycle?

The term "Frontbone" is not recognized as a common type of motorcycle in standard classifications. Motorcycles are typically categorized into various types based on their design and purpose, with options like scooters, backbone bikes, and touring bikes being widely acknowledged.

Scooters are known for their step-through design and are usually smaller and lighter, making them ideal for urban commuting. Backbone motorcycles, on the other hand, refer to a type of frame design that bears the engine and provides structural support, used in various styles of bikes. Touring bikes are designed for long-distance travel; they are equipped with features that prioritize comfort and storage for riders going on extended journeys.

Given that "Frontbone" does not exist in established motorcycle categories, selecting it as the answer identifies an understanding of motorcycle types and terminology.