SEC-imposed restrictions on when a short sale may be executed, intended to prevent investors from destabilizing the price of a stock when the market price is falling. A short sale can be made only when either (1) the sale price of the particular stock is higher than the last trade price (referred to as an uptick trade) or (2) if there is no change in the last trade price of the particular stock, the previous trade price must be higher than the trade price that preceded it (referred to as a zero uptick).