M.S.I.L. stands for Microsoft Intermediate Language. It is also known as Common Intermediate Language .
When a programmer writes a program using a programming language like VB or C#, the compiler of that language converts it into an Intermediate code. This code is CPU independent. Further this code is then sent to CLR or Common Language Runtime(which is the heart of the .NET Framework), where the JIT or Just in time compiler from the CLR, converts it into the native code of the machine.