The AP Stylebook and others are now declaring that "Internet" should no longer be capitalized, that you should just say "internet" instead. This is wrong, because the Internet is just an internet.
Internet is short for internetwork. This was a term developed in the 1970s to describe interconnecting networks together.
There were many internetworks back then. Each major computer manufacturer had its own, incompatible internetworking "protocol". IBM with it's SNA, DEC with it's DECnet, Xerox with XNS, and later Apple with its AppleTalk.
Since it would be nice to interconnect all computers, and not be locked into a single manufacturer, many efforts were taken to standardize internetworking protocols, so that all computers could be placed on the same network. Most people put their support behind GOSIP, the "Government Open Systems Interconnect Profile", a standard created by the biggest corporations and the biggest governments.
However, in 1982, the DoD paid a consulting company to added Xerox's XNS and a research project called "TCP/IP" into an early form of Unix. This form of Unix, called "BSD", was popular among universities. The DoD's goal was to make it easier for researchers who it funded to talk to each other. After this point, universities rapidly started interconnecting themselves together with this "TCP/IP" research project.
They did so for three reasons. The first reason was the way TCP/IP was government, in a libertarian manner, whereby everyone was free to experiment, add new capability first, then officially give working projects the official "standard" seal of approval later. In contrast, the competing GOSIP standard worked the opposite way, where committees debated how things should work for years before a standard was created, before people started working on the features. Everyone today learns the GOSIP standard 7-layer model, but nobody knows what layers 5 and 6 are, because they were never implemented on the real Internet.
The second reason was the source was open. Long before GNU came around and took credit for the idea of open-source, the BSD community had made source openly available to everybody. People could see how TCP/IP worked, and improve it.
Thirdly was the practicalities of TCP/IP's design, namely the "end-to-end" principle. Routers were simple devices, based on simple computers. Thus, adding the necessary routers to connect your university to the Internet was trivially easy. The explosion in commodity computers, the "personal computer" revolution, likewise meant an explosion in commodity routers, since with simple software, every computer could also be a router. It's like how every $35 Raspberry Pi 3 computer is also a WiFi access-point router.
Back in the early 1980s, when all this was going down, there were many globe-spanning internetworks. Even up through the early 1990s, only die hard activists (such as myself) believed the TCP/IP internetwork was the only correct choice. Most business, most government, and most everyone else believed some "real" standard would eventually take over, such as GOSIP.
Then the web happened, and sudden a TCP/IP internetwork became known as the one-and-only Internet that we see today. Those other networks persisted for a time, then withered. There are still die-hard GOSIP loyalists who bitterly defend their crappy alternative as being superior, even though none of them really can explain layers 5 and 6 properly.
But today, we now have a new TCP/IPv6 internetwork which is actually incompatible with the original TCP/IP internetwork. These two internetworks run side by side, on the same wires at the same time, which is my laptop in this coffee shop is connected to both simultaneously, but they are still disjoint networks. Sometimes my laptop can get to Google via the original TCP/IP, sometimes it can only get to Google via TCP/IPv6.
Likewise, corporations and governments still maintain their own private internetworks, like the DoD's SIPERNET, which is based on TCP/IP, but not internconnected directly to the rest of the Internet.
The point is: the Internet is an internet. This history is important. Getting rid of the capitalization gets rid of this history.