Free Agent Auction

Instead of the traditional free agent waiver wire, we'll be trying a new system this year. It's a blind free agent auction or as EPSN calls it, "FAAB."

What is FAAB? It stands for free-agent acquisition budget, a stash of imaginary cash that every team in your league is given to do free-agent auction bidding. (Look at that! Two acronyms for the price of one! What a bargain!) Simply put, FAAB is an in-season salary cap that covers all your free-agent needs.
...
FAAB not only is a far more equitable system -- a team that needs to make several waiver claims because of multiple injuries during a week can actually do so -- but also offers far more in the way of strategy. Knowing when to spend your limited budget while simultaneously trying to feel out your fellow owners as to how much of a bid is "too much" makes for a much more rewarding fantasy experience than waking up in the morning, hearing your star first baseman is out for the year and discovering all of the top free agents at the position have already been snatched up while you slept.
-ESPN, "How to use the FAAB feature"

Some more details:

• The blind auction will run every day Wednesday through Sunday at 11 am EST (So not on Mon and Tue)
• You have $100 for the entire season
• There will be players available for $0
• If you bid $50 for a player and the next highest bid was $20, you still pay $50
• ESPN: How to use the FAAB feature article
• Links to forums where people have asked questions about the feature: link one, link two