.NET framework is the software frame work developed by Microsoft. And it came into existence in the year 2000. It provides a large library and Language InterOperability across many programming languages provided by .NET framework.
-> It’s not a single language; it‘s a collection of multiple languages and multiple  technologies. That‘s why it can be called as ―”platform” (by containing multiple languages and technologies).
->It’s a Network enabled technologies collection. That‘s why it was named as .NET.
There is no any abbreviation for  .NET.
It is used in the development of  various kinds of Applications like:
-> Desktop applications
* Charachter User Interface(CUI)
* Graphical User Interface(GUI)
->Web Applications/websites
->Windows Mobile Applications
-> Windows services
->web services
->WPF applications.NET Framework:

1.  VC#.NET ( Visual C Sharp.NET)
2.  VB.NET ( Visual Basic.NET)
3.  VC++.NET ( Visual C++.NET)
4.  VJ#.NET ( Visual Java Sharp.NET) etc..

1.  ASP.NET  (Active Server Pages.NET)
2.  ADO.NET  (ActiveX Data Objects.NET)
3.  WCF  (Windows Communication Foundation)
4.  WPF  (Windows Presentation Foundation)
5.  WWF  (Windows Workflow Foundation)
6.  AJAX  (Asynchronous JavaScript And Xml)
7.  LINQ  (Language Integrated Query)