What is theme song?

A theme song is a musical composition that is associated with a particular television show, film, video game, or other work. It is typically played at the beginning and/or end of the work, and serves to set the mood and tone of the piece. Theme songs are often written specifically for the work they are associated with, and can become iconic in their own right. Some famous examples of theme songs include "The Simpsons" by Danny Elfman, "Game of Thrones" by Ramin Djawadi, and "Mission: Impossible" by Lalo Schifrin.