What is the difference between an opera and a musical?

Question:

What is the difference between an opera and a musical?

At first it seemed obvious to me, but Operas like the Gilbert and Sulliven operas seem more like musicals while musicals like Phantom of the Opera seem closer to opera.

Best Answer - Chosen by Asker: There isn't much difference. Musicals, like the Sound of Music where there is speaking and singing can be considered operettas, ones like Phantom and Les Miz' where there is constant music and singing are by definition operas. Think of it this way operettas have speaking (the music stops) operas are sung all the way through.