If you read it...
You would know what it means...But since you're too lazy to read it for yourself, here's one paragraph that summarizes it well:
"The selling shareholders identified in this prospectus may sell up to 5,607,468 shares of our common stock. Those shares of common stock were originally issued by us in full satisfaction of such shareholders’ contingent right to certain milestone payments in connection with our acquisition of Systems Medicine, Inc., or SMI, in a stock for stock merger. The selling shareholders may offer and sell their shares in public or private transactions, or both. These sales may occur at fixed prices, at market prices prevailing at the time of sale, at prices related to prevailing market price, or at negotiated prices."
