Zero Plus Tick
Definition of 'Zero Plus Tick'
A security trade that is executed at the same price as the preceding trade but at a higher price than the last trade of a different price. For more than 70 years there was an "uptick rule" as established by the U.S. Securities and Exchange Commission (SEC); the rule stated that stocks could be shorted only on an uptick or a zero plus tick, not on a downtick. This rule was lifted in 2007.
Investopedia explains 'Zero Plus Tick'
For example, if a succession of trades occurs at $10, $10.25 and $10.25 again, the latter trade would be considered a zero plus tick, or "zero uptick", trade.
It was thought that short selling on downticks may have led to the stock market crash of 1929, but the uptick rule was lifted in 2007 after the SEC concluded that markets were advanced and orderly enough to not need the restriction. It is also believed that the advent of decimalization on the major stock exchanges helped to make the rule unnecessary.