An RSS feed includes full or summarized text, plus metadata such as publishing dates and authorship. RSS feeds benefit publishers by letting them syndicate content automatically. They benefit readers who want to subscribe to timely updates from favored websites or to aggregate feeds from many sites into one place.

RSS feeds can be read using software called an RSS reader. The user subscribes to a feed by entering the feed's URL 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 work, downloads any updates that it finds, and provides a user interface to monitor and read the feeds.
-- From Wikipedia

1. Community Custom RSS Feed Builder
2. U.S. Government RSS Library
3. Blogs from the U.S. Government
4. Podcasts from the U.S. Government

OpenSearch is a collection of technologies that allow publishing of search results in a format suitable for syndication and aggregation. It is a way for websites and search engines to publish search results in a standard and accessible format.