Backbone n. : The column of bones in the back which sustains and gives firmness to the frame; the spine; the vertebral or spinal column.

Backbone n. : Anything like , or serving the purpose of, a backbone.

Backbone n. : Firmness; moral principle; steadfastness.

Example:
Why are small business the Backbone of our economy and not corporations?

Taxonomy
Internet backbone, Internet, free encyclopedia, backbone, government, backbone network, Backbone networks, search, nodes, interconnected, high-capacity, capacity data, routes, continents, and oceans, oceans of the world, architectural feature, network state.

Defination from the web:
backbone. From Wikipedia, the free encyclopedia. Jump to: navigation, search. Each line is drawn between two nodes, representing two IP addresses. ... The Internet "backbone" consists of many different networks. ...