The feed relationship can be used to indicate that there is a syndicated feed associated with a web site or page:
<link rel="feed" type="application/rss+xml" href="/feeds/announcements.xml"/>
It can also be combined with the alternate relationship to indicate that the same content is also available as a feed.
<link rel="alternate feed" type="application/rss+xml" href="/blog/rss-feed.xml"/>
One of the most common uses of this is for a feed that a user can subscribe to in order to automatically receive any new entries added to web-based blog pages.