What is the Internet backbone?

The Internet backbone refers to the main "trunk" connections of the Internet. It is made up of a large collection of interconnected commercial, government, academic and other high-capacity data routes and core routers that carry data across the countries, continents and oceans of the world.

Part of the extreme resilience of the Internet is due to a high level of redundancy in the Internet backbone and the fact that the Internet Protocol routing decisions are made and updated in real-time during use.

Source: http://en.wikipedia.org/wiki/Internet_backbone