This is actually an abbreviation for Framework Class Library (FCL).
In July 2000 Microsoft announced the release of its new .NET platform, which represented a major change in the way people think about programming.
This library contains namespaces and classes to support just about everything: input and output, string manipulation, security management, network communication, thread management, text manipulation.
Installing the .NET Framework
If you do not have a the .NET Framework installed you can download it (and install it) FREE of charge from the Microsoft website.
Repairing the .NET Framework
If you need to repair an existing installation then refer to the following article.
Knowledge Base Article (306160)
0318785 - How to determine which versions of the .NET Framework are installed and whether service packs have been applied
0315291 - How to detect the installed version of the .NET Framework in a Visual Studio Setup and Deployment package
- How to detect the version of the .NET Framework that is installed on the computer