Definitely a genre in its own right, the musical encompasses many aspects of the performing arts. Musicals often present the audience with a fantastical look at an otherwise ordinary situation. As with any play, novel or story, the plot can be on a variety of subjects from the 'love story' to the 'hero versus villain' to a 'look into the lives of a certain group of people'.
Songs are usually an extension of the characters and often replace dialogue.
And of course, one can't have songs without dancing. Make-up and hair styles also go hand in hand with the costumes to create a believable character. These are the main designations that make up a musical. Taking away the songs would result in a straight stage play. Although not a big draw in today's market, movie musicals were common in earlier years.