Is Jazz, by definition, a music style wihout vocals?

Answer 1

There can be vocals to jazz and even the spoken word like beat neck poetry. It has a rhythm section and an improvised section. So the singer could be the rhythm section and the piano would then be the improvised section. It's usually done at 4/4 speed (one beat a second).

Answer 2

Jazz by definition covers many styles. Jazz singers often fit into big band or doowop styles. My favorite is bossa nova from brazil. You should check out Antonio Calros Jobim