What is CLR? 

CLR is .NET equivalent of Java Virtual Machine (JVM). It is the runtime that changes a MSIL code into the host machine language code, which is then implemented appropriately. The CLR is the execution engine for .NET Framework applications. It gives a number of services, including:

Code management (loading and execution)

Application memory isolation

Verification of type safety

Conversion of IL to native code.

Access to metadata (enhanced type information)

Managing memory for managed objects

Enforcement of code access security

Exception handling, including cross-language exceptions

Interoperation between managed code, COM objects, and pre-existing DLL's (unmanaged code and data)

Automation of object layout

Support for developer

Services (profiling, debugging, and so on).