Years ago, the accepted consensus seemed to be that a piece of music needed to have melody, rhythm, and harmony....all three.

Of course, this would exclude unaccompanied singers, solo melody players and so on. Therefore, this definition doesn't sit easy with me. Of course, many songs and tunes have their own inherent rhythm which can also be accentuated by individual singers and players.

So, while the melody is the most mportant thing for me, songs or instrumental pieces which are entirely rhythmic could arguably also be described as musical. Therefore, I was probably being a bit harsh re "rap" albeit it's not something that's too my taste. However, I still think of it as a form of poetry which may or may not be performed to a musical backing.