[c#] What does mscorlib stand for?

It stands for

Microsoft's Common Object Runtime Library

and it is the primary assembly for the Framework Common Library.

It contains the following namespaces:

 System
 System.Collections
 System.Configuration.Assemblies
 System.Diagnostics
 System.Diagnostics.SymbolStore
 System.Globalization
 System.IO
 System.IO.IsolatedStorage
 System.Reflection
 System.Reflection.Emit
 System.Resources
 System.Runtime.CompilerServices
 System.Runtime.InteropServices
 System.Runtime.InteropServices.Expando
 System.Runtime.Remoting
 System.Runtime.Remoting.Activation
 System.Runtime.Remoting.Channels
 System.Runtime.Remoting.Contexts
 System.Runtime.Remoting.Lifetime
 System.Runtime.Remoting.Messaging
 System.Runtime.Remoting.Metadata
 System.Runtime.Remoting.Metadata.W3cXsd2001
 System.Runtime.Remoting.Proxies
 System.Runtime.Remoting.Services
 System.Runtime.Serialization
 System.Runtime.Serialization.Formatters
 System.Runtime.Serialization.Formatters.Binary
 System.Security
 System.Security.Cryptography
 System.Security.Cryptography.X509Certificates
 System.Security.Permissions
 System.Security.Policy
 System.Security.Principal
 System.Text
 System.Threading
 Microsoft.Win32 

Interesting info about MSCorlib:

• The .NET 2.0 assembly will reference and use the 2.0 mscorlib.The .NET 1.1 assembly will reference the 1.1 mscorlib but will use the 2.0 mscorlib at runtime (due to hard-coded version redirects in theruntime itself)
• In GAC there is only one version of mscorlib, you dont find 1.1 version on GAC even if you have 1.1 framework installed on your machine. It would be good if somebody can explain why MSCorlib 2.0 alone is in GAC whereas 1.x version live inside framework folder
• Is it possible to force a different runtime to be loaded by the application by making a config setting in your app / web.config? you won’t be able to choose the CLR version by settings in the ConfigurationFile – at that point, a CLR will already be running, and there can only be one per process. Immediately after the CLR is chosen the MSCorlib appropriate for that CLR is loaded.