Brief summary: Morgan oversells the offering. Facebook gives Morgan the right (but not the obligation) to cover its short position by buying shares at the offering price. This is a defensive maneuver.
If the stock pops, Morgan buys the shares from Facebook at the offering price in order to cover its short. Otherwise they'd have to purchase at the market price (which would cause them to lose money). This is the hoped for scenario.
In the unexpected case, where the stock's price trends below the offering price, Morgan covers its short by buying shares directly from the market (instead of from Facebook). This stabilizes the price of the stock at the offering price and ensures that public investors don't go underwater soon after the offering.
It sounds like there are some complicated maneuvers that the underwriter can pull to make some money off the greenshoe (it's not all flowers and sunshine: http://dealbreaker.com/2012/05/facebook-ipo-goes-nowhere-in-...) but this particular implementation seems relatively good to Facebook and the public investors.
Brief summary: Morgan oversells the offering. Facebook gives Morgan the right (but not the obligation) to cover its short position by buying shares at the offering price. This is a defensive maneuver.
If the stock pops, Morgan buys the shares from Facebook at the offering price in order to cover its short. Otherwise they'd have to purchase at the market price (which would cause them to lose money). This is the hoped for scenario.
In the unexpected case, where the stock's price trends below the offering price, Morgan covers its short by buying shares directly from the market (instead of from Facebook). This stabilizes the price of the stock at the offering price and ensures that public investors don't go underwater soon after the offering.
It sounds like there are some complicated maneuvers that the underwriter can pull to make some money off the greenshoe (it's not all flowers and sunshine: http://dealbreaker.com/2012/05/facebook-ipo-goes-nowhere-in-...) but this particular implementation seems relatively good to Facebook and the public investors.