If you request a Web page, that information often has to cross several networks before it gets to you. Those networks that it crosses are called backbones. Without backbones it would be nearly impossible for you to receive the information you asked for. The Internet backbone comprises very high-bandwidth lines interconnected with fast, high-capacity routers. In brief, backbones are high-speed networks that carry Internet traffic.
Commercial backbone providers include PSINet, UUNET, ANS/AOL, Sprint, AT&T, GTE, IBM, and MCI.

In the image below you will notice that major ISPs and smaller networks are connected directly to a backbone ISP. The backbone ISPs are unique in that they carry high-speed connections between them and are ultimately responsible for transporting information over the network. National long-distance carriers or the government generally install backbone lines.

Backbones join at network access points (NAPs). As the name implies, network access points are the entryways to the Internet. For example, think of all the people from around the world who come to San Francisco to cross the Golden Gate Bridge. They all meet up at the toll plaza before crossing. The toll plaza is equivalent to the network access point. It's a universal gateway. Network access points tie various ISPs and the national telecommunications companies. NAP examples include Sprint and Worldcom. They provide routing flexibility, bandwidth savings, and permit reduction of network lengths.
Here are examples of both public and private NAPs.