Namespace or Assembly?

Question

I am getting very confused between Namespaces and Assemblies. Are System.Data and System.Web Namespaces or Assemblies?

I have noticed these

Answer 1

Others have given very good and detailed answers to this question. But I want to point out that when you're not sure, you can look on MSDN. The MSDN library explains very clearly and simply the namespace and assembly in which any given type resides. It even says the name of the file (in System.Data.dll) so there is no ambiguity.