An RSS Feed is data that comes from your website or news site which can be read by browsers even when they are not pointed at the site. You personal feed might come from your weblog, your profile on a business-related social network, or even from a news website you favor. Results from the feed URL you input will be displayed on your directory page, so if you are going to provide one it is best that the feed exemplifies you and your profession.
If you don't have a feed, or just don't know what one is, you can leave it out with no worry.