MSIL
/ˌɛm-ɛs-aɪ-ˈɛl/
n. “The Microsoft flavor of intermediate language inside .NET.”
MSIL, short for Microsoft Intermediate Language, is the original name for what is now more commonly referred to as CIL (Common Intermediate Language). It is the CPU-independent, low-level instruction set produced when compiling .NET languages such as C#, F#, or Visual Basic.
CIL
/ˈsɪl/ or /ˌsiː-aɪ-ˈɛl/
n. “The common language spoken inside .NET before it becomes machine code.”
CIL, short for Common Intermediate Language, is the low-level, platform-neutral instruction set used by the .NET ecosystem. It sits between high-level source code and native machine instructions, acting as the universal format understood by the CLR.