the Internet

The Internet is the single, worldwide network that connects billions of devices — the one your phone joins when it shows a globe icon. The key idea hidden in the name is inter-net: it is not one network but a network of networks, tens of thousands of separately-owned networks (run by phone companies, universities, businesses, governments) that have agreed to interconnect and forward each other's data.

What makes them all one Internet is that they share a common protocol family, the TCP/IP suite, and a common addressing scheme (IP addresses). Each independent network is called an autonomous system; they exchange traffic at interconnection points and agree, through routing protocols, on how to reach every other network. No one owns or runs the whole thing — it works because everyone runs the same protocols and agrees to pass packets along. There is no central switchboard; data finds its own way across whichever networks lie between source and destination.

Be careful with words: the Internet (capital I) is this specific global network. The Web (the World Wide Web) is just one application that runs on top of it — pages and links served over HTTP. Email, video calls, games, and app traffic are other applications. So 'the Internet is down' usually means the network is unreachable; 'a website is down' means one application is failing. The Internet is infrastructure; the Web is one thing built on it.