What is .NET Framework?

Question

And how to implement tracing in .net?

Answer 1

A programming infrastructure created by Microsoft for building, deploying, and running applications and services that use .NET technologies, such as desktop applications and Web services.

The .NET Framework contains three major parts:

the Common Language Runtime. 
the Framework Class Library.
 ASP.NET

Answer 2

The .NET is a Framework, which is a collection of classes of reusable libraries given by Microsoft to be used in other .NET applications and to develop, build and deploy many types of applications on the Windows platform including the following:

 Console Applications
 Windows Forms Applications
 Windows Presentation Foundation (WPF) Applications
 Web Applications
 Web Services
 Windows Services
 Services-oriented applications using Windows Communications Foundation (WCF)
 Workflow-enabled applications using Windows Workflow Foundation (WF)