Microsoft's R2 Naming Scheme
Some new versions of Microsoft software are released with the "R2" designation.
Although Software Assurance (SA) customers will automatically get rights to R2 releases as part of their subscriptions, customers who purchase license-only Windows Server and other products that are later updated to R2 versions will need to purchase a new license before they can upgrade. In other words, an R2 version is a new version, not just a service-pack level upgrade.
Another aspect of the R2 versions is that although they are treated as new versions for licensing purposes, the R2 versions of server applications will not need new Client Access Licenses (CALs), which would be expected for a new version. A customer would use the same CALs as they were using for the pre-R2 version. Microsoft does not release new CAL licenses to correspond to an R2 server license upgrade.