Called "Twitter #music" (and yes, the hashtag is intentional), #music is described as follows:
A fresh approach to finding new music by using Tweets and follows to power discovery.The idea, therefore, is to use social discovery methodology to propel #music. Naturally, Twitter's #music will only use tweets.
The most popular new music and emerging talent on Twitter right now.
Follow your favorite artists and see which artists they follow.
The app -- free, as you'd assume -- and the underlying service will provide information and news as well, so by following groups and artists, users can keep up to date, which will then, of course, lead to more discovered music.
The songs on Twitter #music are sourced from three services: iTunes, Spotify or Rdio. The default settings are to source previews from iTunes when a user is exploring music in the app. Subscribers to Spotify and Rdio can login to their accounts and listen to full tracks from those respective catalogs.
In other words, Twitter #music is not about listening, but discovering. If you don't have an Rdio or Spotify account, you won't be doing any rocking out.
Twitter added that it is continuing to try to sign deals with other providers.
Both the iOS version and the Web version are currently live. It's unclear when or even if Twitter will release an Android version, but with Android's global dominance, we'd expect it.