What is a node?

ANYTHING which is organized into a hierarchy has nodes:
Code:
                     a
         +----------  --------+
          b                    c
                       +------  -------+
                        d               e
Each one of {a-e} are nodes

A would be known as the Root node,
B,C would be intermediary nodes
D,E would be end-points

In the context of your question (the Internet) the number, names and locations of the
'Backbone' nodes is not easily determined.
 
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