What is a node?

[jlewis]

What is a node? How many nodes are currently connected to the backbone?

 

[DelJo63]

ANYTHING which is organized into a hierarchy has nodes:

                     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.