In classical music, the term is associated with opera. In opera, the star singers often have a much higher billing than any of the other participants in the performance, including the conductor of the orchestra. Some opera roles have high notes, such as high "C" notes for sopranos, that are hard to hit in a live performance. As such, the audience enjoys going to see the performance and find out if their favorite performer will be able to sing these high notes with accurate pitch, strong projection, and a clear tone. In this sense, the high notes sung by the opera singer are the "money notes" that the audience is paying to see, and for which the opera singer commands their high salary.