It floated only a small portion of its stock, making it more vulnerable to price volatility, but questions linger about Groupon's competitiveness in the crowded market for discounting online.

ECONOMIST: Business this week

It promises to buy and sell the stock at the best going price and to trade even when stock price starts to get out of whack, to smooth out volatility.

FORBES: GM Gives High-Freq Firm The Keys

Get a sense of how volatile a company's business value is by looking at volatility in the stock price.

FORBES: Default-risk bookies

The run up in the price of the underlying today as well as the rise in implied volatility on the stock seem to have set the stage for the massive position initiated in AEO options.

FORBES: Bullish Options Speculators Step Into Emulex, Amkor, American Eagle