Theme music is a piece that is often written specifically for a radio program, television program, video game, or movie and is usually played during the intro, opening credits, and/or ending credits. The phrase theme song or signature tune may also be used to refer to a signature song that has become especially associated with a particular performer or dignitary, often used as they make an entrance. The purpose of a theme song is often similar to that of a leitmotif. Such songs can also be used in other ways. One author has made extensive use of them in an effort to explore the feelings behind world views.