That's a really good question. Microsoft has branded so many things with the .NET label that it's difficult to tell sometimes. Let me tell you what it means to me. First, the high-level view:
.NET is a set of technologies that
Pulls together the best of the many disparate application development technologies, particularly those related to Web development.
Unifies today's isolated Web applications and platforms.
Dramatically improves developer productivity.
Makes the same software design best practices available to Web developers that have been used successfully on other platforms for years.
Provides a safe environment in which applications can run without having to concern themselves as much with resource management or low-level programming ...