the Common Type System (CTS) is a standard that specifies how type definitions and specific values of types are represented in computer memory. It is intended to allow programs written in different programming languages to easily share information.

Common Type System (CTS) describes the datatypes that can be used by managed code. CTS defines how these types are declared, used and managed in the runtime. It facilitates cross-language integration, type safety, and high-performance code execution.

.NET is language-agnostic, which allows programmers to write code in different languages (which can be compiled to IL), and that code can interact with other code written in different languages.
Common Type System (CTS) describes the datatypes that can be used by managed code.
The CTS defines the predefined data types available in IL so that all languages that target the .NET Framework can produce compiled code ultimately based on these types.
It provides an object oriented model & also provides a library that contains primitive data types.
CTS defines how these types are declared, used and managed in the runtime. It facilitates cross-language integration, type safety, and high-performance code execution.
CTS deals with the data type. So here we have several languages and each and every language has its own data type and one language data type cannot be understandable by other languages but .NET Framework language can understand all the data types.