base class library (.NET) (BCL)
Base Class Library(BCL) is the class library for the . NET framework that can be accessed using the various .NET programming languages.
The .NET class library, .NET Framework Class Library( FCL), includes many namespaces described in the form System.Forms. The namespaces include those for system configuration (System.Configuration), IO functions (System.IO), diagnostic tools (System.Diagnostics), runtime (System.Runtime), and more.