I see a lot of programming languages had been upgraded to another versions and change their names to "anything.NET", what does .NET refer to?

.NET is a framework which is shared by couple of languages - such as C++.Net, C#, J#, VB.Net, ASP.Net, X++, etc. - , which shared same libraries and comiplation engines.

First i wan't to confirm "Muhammed Sallout's" point ,And i want to add another point i'am not really sure about is that .net languages are compiled in two stages ,, First they are compiled into byte code then they are executed

yes its combination of two files

.NET is a framework exactly a collection of Files that Contains Namespaces And Runtime Instructions Shared by these Programming Languages that you mentioned Before .NetFramwork Each Language has it's Own Library Or Files .

.NET means use .net  Framework , .net  Framework is a software framework developed by Microsoft that runs primarily on Microsoft Windows. It includes a large library and provides language interoperability .

.net  Framework Representsa link betweenthe program and the operating system it is help programer to work with differents operating systems by one syntec code

.NET Framework family also includes two versions for mobile or embedded device use. A reduced version of the framework

c'est facile a comprendre tout simplement il est relier avec tout les produits qui marche sur la mémé base de Runtime ou bien framework de  Microsoft :) techniquement qui doit s’exécuter sur CLR (common language runtime ) de Microsoft 

I believe that the answer you looking for is all the ".NET" 's based on Internet Protocols and standarts and their library helps alot to work fine with any OS.

.NET is a framework or you can say that it is a platform, which is innovation of Microsoft and here you can code a project in the language you are comfortable. It gives great freedom to the developers.

.NET is Microsoft's innovative strategy to simplify building XML Web Services and to develop, deploy, and maintain desktop, enterprise, Internet and Smart devices applications in the Internet age.The .NET platform is thus a runtime environment on which applications coded in any of the managed languages run. It acts as a software layer between the applications written on the .NET and the operating system. For the time being, the operating systems can be any of the Windows platforms.