Earlier it was called Android Market. Google Play was launched again in this month to let Google sell its content not only to Android owners but to anyone. Apart from Android apps, Google Play apps run on number of devices.
In Android market users were only allowed to access Android Apps (outside US) but now Google has expanded its android marketplace which now includes Android Apps, ebooks, movies, as well as music. All these services are divided in four categories respective to their types. To create more awareness about this service Google has embedded Google Play in the Top Black Navigation Bar.