An HD motorcycle refers to the Harley-Davidson motorcycle. Harley-Davidson is the fifth-largest motorcycle company in the world, as of 2015. The company is famous for their iconic engine sound and loyal fan base. The licensing of the Harley-Davidson logo accounted for almost 5 percent of its revenue in 2014.
Harley-Davidson began in 1903 by William S. Harley and Arthur Davidson. Popular models of the company's motorcycles include the Street series, the Sportster, the Touring, the Softail and the S series. The company offers the option for riders to build their own motorcycles through the comprehensive Harley-Davidson website. The company also hosts hundreds of events and rallies throughout the year.