From Wikipedia: "Tap dance was developed in the United States during the nineteenth century, and is popular nowadays in many parts of the world. The name comes from the tapping sound made when the small metal plates on the dancer's shoes touch a hard floor. This lively, rhythmic tapping makes the performer not just a dancer, but also a percussive musician (and thus, for example, the American composer Morton Gould was able to compose a "concerto for tap dancer and orchestra")."
