Q:

What is the difference between a musical and a rock opera?

I've seen multiple works from Andrew Lloyd Webber referred to as "musicals" in some sources, and "rock operas" in others. For most people it seems the two terms are completely interchangeable.
Is there a clean definition and distinction between the two?

A:

The key difference between a musical and an opera is that a musical contains spoken word. While a musical alternates singing with "regular" acting, an opera's story is completely conveyed through singing. Of course, an opera may have a few spoken lines here and there, and a musical may have a very high singing versus speaking ratio. You can already tell what I'm getting at: the line between opera and musical is sometimes fairly thin. And as usual when the distinction between two words is a little bit vague, these two words start being used interchangeably, and often not in a correct manner.

