What is a IL(Intermediate Language)

(IL)Intermediate Language is also known as MSIL (Microsoft Intermediate Language) or CIL
(Common Intermediate Language). All .NET source code is compiled to IL. This IL is then
converted to machine code at the point where the software is installed, or at run-time by a Just-In-Time (JIT) compiler.
Microsoft Intermediate Language (MSIL) is a platform independent language that gets compiled into platform dependent executable file or dynamic link library. It means .NET compiler can generate code written using any supported languages and finally convert it to the required machine code depending on the target machine.
The main advantages of IL are:

1. IL isn't dependent on any language and there is a possibility to create applications with modules that were written using different .NET compatible
languages.
2. Platform independence - IL can be compiled to different platforms or operating systems.

A detail example is available here.