An RSS (Really Simple Syndication) feed is an online file that contains details about every piece of content a site has published. Each time a site publishes a new piece of content, details about that content—including the full-text of the content or a summary, publication date, author, link, etc.—are automatically generated in the file and displayed in reverse chronological order.
RSS feeds are typically coded in XML format.
An RSS reader is an app that parses the XML code of an RSS feed and renders it to look more like what you’d see on a website.