The Common Type System (CTS)
To support multiple programming languages on a single CLR and have the ability to reuse the FCL, the types of each programming language must be compatible. This binary compatibility between language types is called the Common Type System (CTS).
The built-in types are represented as types in the FCL. This means that a C# int is the same as a VB.NET Integer type and their .NET type is System.Int32, which is a 32-bit integer named Int32 in the System namespace of the FCL. You'll learn more about C# types, type classification, and how C# types map to the CTS in Chapter 4.