A Usenet abbreviation, still sometimes seen on for-sale or marketplace boards. Rather than selling an item directly, the user will put it up for auction on a site such as eBay, and then direct users to the web site for bidding. Hence, subject lines in the form "FA: (item)" where (item) is whatever is being auctioned.
Generally frowned upon by old-timers, as it delays the sale for up to a week unless someone chooses "Buy it Now!" from the auction site if available. Also, if few bids come in, the item's owner will often post such messages repeatedly in desperate hopes that someone will take his import Game Boy Advance for more than five bucks.