Common Language Runtime [CLR]

Let's rewind our mind to ancient era, when there is no existence of CLR concept, what happened when we invoke the language program or code. Basically, languages consist both compiler and runtime environment. Compiler converts or compiles code to executable files [known as PE (Portable file) files], which can be run by the users, in the other hand runtime environment provides O.S. [Operating System] services to executable code. Now at that time each language has its own runtime environment. Like Visual Basic contained MSVBVM60.DLL, Visual C++ contained MSVCRT40.DLL and for Java we need JRE [Java Runtime Environment] or JVM [Java Virtual machine].
But, with the invention of Common Language Runtime there is no need to gather individual runtime environment for individual languages, that's why .Net runtime is known as Common Language Runtime [CLR] Environment.