From Wikipedia:

RSS is a family of Web feed formats used to publish frequently updated content such as blog entries, news headlines, and podcasts in a standardized format. An RSS document (which is called a “feed”, “web feed”, or “channel”) contains either a summary of content from an associated web site or the full text. RSS makes it possible for people to keep up with web sites in an automated manner that can be piped into special programs or filtered displays.

The benefit of RSS is the aggregation of content from multiple Web sources in one place. RSS content can be read using software called an “RSS reader”, “feed reader” or an “aggregator”, which can be web-based or desktop-based. A standardized XML file format allows the information to be published once and viewed by many different programs. The user subscribes to a feed by entering the feed’s link into the reader or by clicking an RSS icon in a browser that initiates the subscription process. The RSS reader checks the user’s subscribed feeds regularly for new content, downloading any updates that it finds and provides a user interface to monitor and read the feeds.

The initials “RSS” are used to refer to the following formats:

• Really Simple Syndication (RSS 2.0)
• RDF Site Summary (RSS 1.0 and RSS 0.90)
• Rich Site Summary (RSS 0.91).

RSS formats are specified using XML, a generic specification for the creation of data formats. Although RSS formats have evolved since March 1999, the RSS icon (”“) first gained widespread use in 2005/2006.