A feed is an easy to use way of keeping up to date with lists of information on the web.
You normally subscribe to a feed using a feed reader which collects together all the feeds you subscribe to and also provides a way of unsubscribing should you get tired of a feed. Many browsers have feed readers built in, as do most email clients. In fact, a good way of thinking about feeds, is as a cross between subscribing to an email newsletter and regularly visiting website's news section.
I'm from Volunteer Centre Brighton & Hove and have volunteered here for 2 years, I'm also employed as Volunteering Network Developer which involves developing the use of social networking (e.g. Facebook & Twitter) at the VC.