Details are coming in this morning. A post has been published to Twitter's blog with a lot of information. The Twitter #Music app will help you discover music based on what's trending on Twitter, bands and others you follow and music gleaned from tweets. Basically, a music recommendation service based on tweets!
According to Twitter, it pulls music from iTunes Rdio or Spotify. Music previews will default to iTunes, and those who subscribe to Rdio or Spotify can log into their accounts and enjoy full tracks as they're available. Twitter notes that other music services will be added in the future.
It's going to be fun to play with and we'll have a detailed look at #Music soon.