What is the difference between the internet and the web?
The internet is the global network of connected computers. The web is one service that runs on it. The web is part of the internet; the internet is far more than the web.
The internet is infrastructure — physical and logical. Cables, including the submarine cables carrying the overwhelming majority of intercontinental traffic, plus routers, exchanges, satellites and wireless links, all connected by a shared set of protocols, principally TCP/IP.
Its job is moving packets of data from one machine to another. It does not care what the data means.
It dates to the late 1960s, growing from ARPANET, with TCP/IP standardised in 1983.
The web — the World Wide Web — is an application built on top. It consists of documents identified by URLs, transferred using HTTP, and written in HTML, viewed in a browser.
It was invented in 1989 by Tim Berners-Lee at CERN — twenty years after the internet existed. This gap is the clearest evidence they are different things: the internet ran for two decades without the web.
Other things running on the internet that are not the web:
Email, using SMTP, IMAP and POP — older than the web and entirely separate, even though most people now access it through a browser.
Messaging apps, most of which use their own protocols.
Video streaming and calling, frequently using protocols other than HTTP.
File transfer, online gaming, VoIP, DNS, and the vast machine-to-machine traffic of APIs and IoT devices.
Why the distinction matters practically:
Outages differ. A website being down is not the internet being down. Your connection failing is different from a service failing, and the diagnostic steps differ.
Regulation and governance operate at different levels — network neutrality concerns the internet layer; content moderation concerns services on top.
Terminology. "The web" strictly means browser-accessible pages, so an app that talks to a server is using the internet and not necessarily the web.