FFA = Free For All
They used to be popular and were a way for spammers to harvest email addresses. What happened is that people would prey on unsuspecting webmasters who would pay $30 or so for a service that claimed to submit a website to thousands of search engines. Those search engines were FFA pages. Those pages automatically added the newest link at the top of a page. Search engines started penalizing webmasters for doing this, and a lot of sites were banned.
If you ever hate someone and want to piss them off, sign them up for some ffa links, their email address will be flooded within a day.