The .NET Framework is a development and execution environment that allows different programming languages & libraries to work together seamlessly to create Windows, Web, or Mobile applications that are easier to build, manage, deploy, and integrate with other networked systems or as stand alone applications.
The .NET Framework consists of:
The Common Language Runtime (CLR)
A language-neutral development & execution environment that provides services to help "manage" application execution
The Framework Class Libraries (FCL)
A consistent, object-oriented library of prepackaged functionality