What is CLR (Common Language Runtime) in the .NET framework

• The Common Language Runtime is responsible for executing your application code.
• In .NET, source code is never compiled directly into the machine code. Instead the compiler converts the code into an intermediate language called MSIL(Microsoft Intermediate Language).
• MSIL is a low-level, platform independent language.
• Whenever your application executes, the MSIL code is "just-in-time" compiled into machine code by JIT compiler. 
• JIT compiler is responsible for converting your MSIL code into machine level language for its execution.
• So, in reality the .NET framework understands only one langauge and that is MSIL.
• However you can write applications using different languages such as VB, C#, J# etc.