What is a Feed? you ask...
A content feed is a web page that is designed for computers. Special computer programs (these are often called feed aggregators or feed readers) can read this web page and show you the new items as they appear.
Web Content feed, are somtimes called RSS Feeds or ATOM Feeds these are technical names that describe what standard the feed is using. You don't need to pay attention to ATOM vs RSS all feed readers know how to read both feeds.