Define "the Internet"

This is a question. I don't know the answer to it myself so I ask you.

I know what the internet protocol is - it's as defined in RFC791. I, therefore, also know what an internet(work) is. I understand what we mean by the Internet, but I am unable to define it, with all my knowledge of networking and network protocols as a graduate student. As a consequence, I am also unable to define the World Wide Web, the definition of which depends on that of the Internet.

The best definition I can come up with is this:

"Internet is that inter-network which has the most nodes (hosts + gateways/routers) in the world that run the internet protocol (RFC791) to inter-connect."

Please contribute if you can provide a better definition.