Common Type system Describes the datatypes that can be used 
by managed in the run time .

it facilitates 
* Cross Language integreation
* Type safety
* High performance and code Execution

Common Type System is a set of rules and standard that a 
language must adhere in order to a language compatible.

Example
1) An integer variable in C# is written as int, whereas in 
Visual Basic it is written as integer. Therefore in .Net 
Framework you have single class called System.Int32 to 
interpret these variables. 
2) For the ArrayList data type .Net Framework has a common 
type called System.Collections.ArrayList. In .Net 
Framework, System.Object is the common base type from where 
all the other types are derived.

CTS stands for common type system.

On .Net Framework there are several predefined libraries 
are present which are common for all language i.e the 
library which is used by vb.net the same can be used by 
C#,common for all.because of this we can take lase 
time,less space and so on . this concept is known as cts.