This release of Solaris is called Solaris 7 instead of Solaris 2.7. As the Solaris product line continues to grow, this name change will make it easier for you to determine which products in the Solaris line you might want to use.
In Solaris 7, the transition to the new name change is in progress. That means that you will still see references to Solaris 2.7, and even to Solaris 2.x.
The name of the core operating system has not changed. In this release, it is SunOS 5.7.