A long time ago every website was closed off. There was no way to know if a website was updated other than to go there. There were various attempts to come up with a way to more easily syndicate content but none were easier or more popular than RSS.
Wikipedia: RSS (RDF Site Summary or Really Simple Syndication)  is a web feed  that allows users and applications to access updates to websites in a standardized, computer-readable format. These feeds can, for example, allow a user to keep track of many different websites in a single news aggregator.
It looks like various people were involved over the years with different versions. It was originally built for a part of Netscape.
RSS is still around but I’m saying I miss it because it’s not everywhere like it once was.
It used to be in every web browser, and all major websites, such as Twitter, provided feeds. Then you would install a feed reader on your computer or join a website that let you subscribe to RSS feeds. So, you could go to a Twitter profile click a button in your browser and subscribe. Any new post would show up in your feed reader.
That alone is nothing special but with RSS you also can subscribe to any news site or blog that provides a feed. This means you have a one stop shop. You have one place that alerts you anytime your favorite websites update.
The most popular blogging tools like WordPress still come with these feeds by default. Since currently 20% to 40% of all websites run on WordPress, there’s a good chance your favorite site still offers RSS. That’s the good news.
The bad news is there has been an assault on RSS by the big web companies.
As soon as it got really popular, Twitter removed RSS. Other major social media sites did the same. Slowly web browsers removed the capability to subscribe to feeds with one click.
Seriously? As soon as the Internet becomes a truly very connected, easy to subscribe to most anything, beautiful thing, people got greedy and decided it was too much. I mean, why let people super easily read multiple tweets, blogs, and news all in one place? Or, why have one standard that alerts people about new content? That would mean Internet companies would not be able to offer proprietary solutions and keep you in their app or on their site… forever! 👹
The trend has crept into new software and new web building technologies. Sometimes depending on what you are building your website with it is harder than ever to add RSS feeds. Your best bet is to just use WordPress.
Side note: I don’t care if it’s RSS, ATOM, or a new JSON format. The point is that it should be as standard as HTML to have a text feed in all websites which is popular enough to where there are enough apps to consume it. I mention this last part because sure, sites that don’t have RSS may have a public API. A JSON feed. But, each may be a little different. It’s not as standard and simple as RSS/ATOM came to be.
I have a feed for this blog although I don’t think anyone would be interested in subscribing. ☺️
For a few years now I’ve heard whispers of a RSS resurgence. And maybe in some circles is has come back or will. But, the only way it would be mainstream again is if people gave up social media (which despite the name is only social inside of their platform due to not offering RSS).