Vijay Iyer, speaking with Christopher Lydon on the Open Source podcast:

When we say [music is] a conversation, that’s being employed as a metaphor. When we think linguistically about conversation we think about the transmission of information. But that’s not all that conversation is. What it is first is music, which is to say it’s a way of harmonizing with one another. So using the conversation metaphor for music is a little bit backwards to me, because really music came first. That’s the sound of us being together. That’s what music is. So conversation is inherently musical, because it’s about harmonization with another person, it’s about grooving with another person, it’s about improvising. It’s all those things already.

Iyer turns the traditional language metaphor on its head by saying that spoken language mimics music, not the other way around. If I were looking for a definition of “jazz” in the 21st (or any) century, I’d say he’s on to something here.