Naked Short Selling
The sale of shares one has neither borrowed nor made arrangements to borrow. Under Regulation SHO, investors engaging in naked shorting much abide by a "locate" requirement and a "close-out" requirement. The locate requirement forces brokers to have reasonable grounds to believe that the short-sold security can be borrowed; the broker must document this prior to the security's sale. With some exceptions, the close-out requirement means that brokers who have failed to deliver a short-sold security for 13 days must purchase similar securities and present those instead. Naked shorting is very high risk.
The investment position of the underwriting firm for a new issue when the underwriting firm has sold more shares short than will be issued. A short position prior to the issue permits the underwriter group to stabilize the price of the stock by becoming buyers immediately following the deal. A naked short allows the underwriting firm greater stabilization ability. See also greenshoe.