Modern, Show tunes, and Broadway
A show tune is a popular song originally written as part of the score of a "show" (or stage musical), especially if the piece in question has become a "standard", more or less detached in most people's minds from the original context. Particular musicals that have yielded "show tunes" include:
Though show tunes vary in style, they do tend to share common characteristics—they usually fit the context of a story being told in the original musical, they are useful in enhancing and heightening choice moments.
Show tunes were a major venue for popular music before the rock and roll and television era; most of the hits of such songwriters as Jerome Kern, Cole Porter, and George Gershwin came from their shows. Although show tunes no longer have such a major role in popular music as they did in their heyday, they maintain somewhat popular, especially among niche audiences. http://en.wikipedia.org/wiki/Show_tunes