High-speed networks that carry Internet traffic.
These communications networks are provided by companies such as AT&T, GTE, IBM, MCI, Netcom, Sprint, UUNET and consist of high-speed links in the T1, T3, OC1 and OC3 ranges. The backbones carry Internet traffic around the world and meet at Network Access Points (NAPs).
Internet Service Providers (ISPs) connect either directly to a backbone, or they connect to a larger ISP with a connection to a backbone.
The topology of the "backbone" and its interconnections may once have resembled a spine with ribs connected along its length but is now almost certainly more like a fishing net wrapped around the world with many circular paths.