The Android Market, or "the Market" as many call it, is a staple to Android device owners, but Google wants to expand usage of it and some of its other services by rebranding it's Books, Music, and Movie ventures into one unit with the Android market. This new suite is known as Google Play (Play Store, Play Music, Play Movies, and Play Books). The name "Play" was speculated as the new Google tablet that is thought to be in development behind the doors over at Google, but obviously that was some incorrect info as play is the new "Market". This move to rebrand it's services comes after a Google exec mentioned a few days ago that Google Music hasn't taken off like they had hoped, but it seems that Google may have wanted to "free" it's music and other services from the Android name with this rebranding. Not that associating with Android is bad, but not having the name gives them more freedom with the service.
In my own opinion we may see Google go mainstream with the new market at least on the movies and music side and offer it to those without Android devices which would open them to a much larger market and possibly help their services expand to start competing with iTunes and Amazon in terms of Digital content sales. However, based on the new promo video they released it seems that their primary selling point, at least for now, is to unify your content into one seamless wireless syncing experience that keeps all your content ready on all devices. Google is taking a shot at Apple as this is what iCloud is supposed to do even though I still haven't heard many people that have managed to get it to do everything it is supposed to do. Anyways the video is below if you want to see Google tell you in their own words.