They are(simply put) the things that you import....

EXAMPLE:

VB

Import (namespace)

C#

Using (namespace)

Here's one: there's no namespace in C

profile namespace

Of course! All namespaces are nested by default since all namespaces exist in the global namespace. A class is also a namespace; therefore classes can also be nested.

A public function is scoped to the class in which it is declared. If declared non-static, then it must be invoked against an instance of the class but if declared static then namespace resolution is required to access the function.

A non-member function is not scoped to any class but may be scoped to a namespace. If no namespace is specified, then it is scoped to the (unnamed) global namespace. If scoped to any other namespace then namespace resolution is required to access the function.