IL, CIL, and MSIL all refer to the same concept with slightly different naming depending on context in the .NET Framework ecosystem.

• IL (Intermediate Language): A general term for the low-level, CPU-independent instruction set generated by .NET compilers.

• CIL (Common Intermediate Language): The official name defined by the CLI (basketball stars Common Language Infrastructure) specification.

• MSIL (Microsoft Intermediate Language): The older Microsoft-specific name for the same thing, used before standardization.

In practice, they all describe the intermediate code produced when you compile languages like C# or VB.NET. This code is later compiled into native machine code by the JIT (Just-In-Time) compiler at runtime.

The .NET application, respective language compiler compiles the code and converts our code from high language into Intermediate language (IL). This IL is also called as Common Intermediate language (CIL) and Microsoft Intermediate language (MSIL).