Libretto – the overall text including the spoken and sung parts
Lyrics – the words to the songs

Most song in Musical Theatre are either:
Action songs, which move the plot forward or

Character songs, which enable a character to express their feelings
Within these two formats, different song types can be found including:

Ballads, which are usually slow, romantic and reflective
Comedy songs , which are funny, so the lyrics are very important
Production numbers, which involve the full company and are used to show major changes in location or plot, and often open and close acts

Rhythm songs which are driven by energetic rhythm patterns

Although most musicals use dialogue some are thought composed. There is little or no dialogue, nearly everything is sung.