Explain the concept of CLR ?

The most important component of the .net framework is the CLR or the Common Language Runtime. The CLR manages and executes code written in .net languages. It activates objects, performs security checks, lays them out in memory, executes them and garbage collects these objects as well.
The CLR is a runtime engine that loads required classes, performs just in time compilations, enforces security checks and a bunch of other runtime functions.
The CLR executables are either exe or dll files that consist mostly of metadata and code. These executables must adher to a file format called the Portable Executable (PE) file format