The Internet is often described as a network of networks because it is made up of millions of interconnected computer networks that communicate with each other. These networks can range from small local area networks (LANs) to large-scale wide area networks (WANs) operated by Internet Service Providers (ISPs), organizations, and data centers.

The key idea behind the Internet being a "network of networks" is that it enables the exchange of data and information between different networks, using common protocols like TCP/IP (Transmission Control Protocol/Internet Protocol). This allows devices and systems, regardless of their location or the type of network they belong to, to connect and communicate with each other globally.

In short, the Internet is a vast, global system that connects countless smaller networks together, making it possible for users to access websites, send emails, share files, and interact in many other ways online.