RSS stands for Rich Site Summary (or Really Simple Syndication, take your pick). In a nutshell, RSS is a way for people who publish content online to notify who are people interested in that content whenever fresh content is made available online.
This site, Interglacial, used to host RSS feeds for over two dozen sites, when those sites were still using site frameforks didn't yet support RSS. Now sites that want to publish RSS feed, just turn on that option in their software. Often, there is also an RSS for watching individual threads or topics in message bases / discussion areas / etc.
Most of the sites that I generated feeds for have "moved on"-- no new content for several years, or the site simply goes away, or my RSS generator program can no longer make sense of the site enough to make an RSS for it. I'm calling those "dead feeds" and setting their "farewell" final message to say that this is a dead feed so kindly remove it from your program.
As I write this in 2023, RSS feeds, and programs that read them, are still alive and well (trust me, I see my server logs!), but people/sites/etc that want people to see new content, post it to social media.
I won't be adding any new feeds. Many sites autogenerate RSS feeds of their own, as part of the system for adding new posts.
Note: I've set the metadata in RSS files to say how often they change (if at all). If you have an option to say how often to poll, but the site says "weekly" (for example), please don't set it for anything more frequent than daily.