A concert tour (or simply tour) is a series of concerts by an artist or group of artists in different cities, countries or locations. Often concert tours are named to differentiate different tours by the same artist and to associate a specific tour with a particular album or product. Especially in the popular music world, such tours can become large-scale enterprises that last for several months or even years, are seen by hundreds of thousands or millions of people, and bring in millions of dollars in ticket revenues. A performer who embarks on a concert tour is called a touring artist.