Today's era is the age of mobile data and the internet where both mobile data and the internet is not a final product but the source or means of creation of other final products which will rule the market with the help of these medium.
It is my opinion that the definition is in the eye of the beholder. By this I mean that it depends on the use made of them as tools. If you are considering the communications protocols used for various legs of the Internet, you get a different answer than if you are considering an Enduser view who does not care how they communicate, just that they can reliably. However, if you are considering End to End data it becomes more complex, because you have to insure data integrity issues like spoofing and steganography which can introduce problems. Again to me it appears that it is not just the ability to communicate (with or without integrity issues), but the ability to generate real understanding.
The Internet is a two-way global telecommunications system. A more modern and more flexible version of the global telephone system, which is also a two-way communications system, the most similar system we used to have to today's Internet.
(When I say two-way, I'm saying that it allows all users of the system to transmit and to receive. Unlike, say, radio and TV, which only permit the users to receive information.)
Telephone was designed to carry voice. The Internet can carry text, graphics, voice, full-motion video, really any type of binary files. For example, these days, I listen to radio and watch TV over the Internet, rather than the old way. Radio and TV stations have web sites, you can use those instead of using the over-the-air signals.
Tiktok and Facebook, Amazon, many radio stations and TV stations, medical practices, and so on, those are businesses that use the Internet medium. Just like, your local food market depends on the public road network to provide customers access to the store, correct? Well, Facebook, Amazon, and a huge number of other businesses, depend on the Internet to provide customers access to their business.
Sometimes the business can rely 100% on the Internet for everything to sells. Other times it may also rely on a delivery service. Other times, let's say in the medical field, the Internet may be used mostly for scheduling appointments, talking to your doctor, getting results, but the patient usually has to go to the doctor's office in person to be examined by the doctor or other practitioner.