What is "underbone"

n. A small motorcycle built on a frame consisting mostly of one large-diameter tubular component.

An underbone cycle may share its fuel tank position and tube framing, along with fitted bodywork and splash guards with a scooter while the wheel size, engine position, and power transmission are like those of conventional motorcycles.

Unlike motor scooters, underbones are mostly popular in Asia, particularly in Southeast Asia, Middle East, India, Taiwan and China, as well as some parts of Eastern Europe and Russia.