.Net is a Framework
a sandbox for runtime too
a memory manager for its app running on it.
a unification in Microsoft Technology ( Phone / Desktop / Web / free technologies )
a container for one runtime
a handler for managed code based on .Net itself
a MSIL, kind of bytecode from Microsoft
a bunch of common resources of codes and shared libraries
a C/C++/C# compiler
a gate for Php / Python / Linux exploitation by Windows
a nest for ASP
a check-point for compliant code to kernel
a run time for uncompliant code too
a good idea for IT workers