A rule of the Securities and Exchange Commission (SEC) that says that all short sales have to be made in a rising market. In other words, a short sale can occur only if the last transaction was at a higher price than the previous sale (uptick or plus-tick). If the last sale price is unchanged but still higher than the last preceding different transaction (zero-plus tick), then a short sale can still occur. The short-sale rule also is called the plus-tick rule.