The .NET Framework provides a run-time environment called the common language runtime (CLR) , which runs the code and provides management services (such as security and exception handling) that make the development process easier. Programs written for .NET Framework execute in the CLR software environment that is part of .NET Framework.
The CLR version number included in a .NET Framework version is not necessarily the same. For instance, .NET Framework versions 4 and 4.5 includes the CLR version 4. Refer to online documentation provided by Microsoft to learn more about .NET Framework and CLR.