Backbone
In general usage, the backbone is a synonym for the spine of an animal. It is also slang for "courage".
In telecommunication, the term backbone has the following meanings:
- The high-traffic-density connectivity portion of any communications network.
- In packet-switched networks, a primary forward-direction path traced sequentially through two or more major relay or switching stations.
Source: from Federal Standard 1037C and from MIL-STD-188