RSS stands for Remote Site Syndication. It is the standard defined for podcasts (and news stories, etc.) It is a list of all the episodes, along with descriptions, metadata and where to download them. If you use a podcasting app, this is what it subscribes to when you subscribe to a podcast.

If I post an RSS url, it will automatically open your podcast app when you click on it:

rss://anchor.fm/s/91b8fbc8/podcast/rss

Main stream podcasting sites often make these links difficult or impossible to find (Fuck you Apple.)