In Internet, most computer are not connect directly to the Internet. Rather they are connected to smaller network, which in turn are connected through Gateways to the Internet Backbone.
Two new terms you have encountered just now – Gateways and Backbone. Let’s define:
A Gateways is a device that connects dissimilar networks. A Backbone is central interconnecting structure that connects one or more networks just like the trunk of a free or the spine of a human being.