The Common Type System is just a set of rules that defines a commonly used set of primitive types, like System.Int32, that are used by all languages that the Common Language Runtime supports. These type are mapped to the types used in each language. For example, System.Int32 is an int in C# and an Interger in VB.NET. This makes it very easy for classes written in different languages to pass data back and forth without any custom, time-consuming, conversions. The CTS is a set of rules, or specifications, at the core of the CLR, not a module or a component. It's part of the Common Language Specification that every .NET compiler MUST adhere to to manitain compatibility with the .NET Framework.
Dave Kreskowiak Microsoft MVP - Visual Basic