A transaction/ trade that takes place at the same price level of a previous transaction/ trade, but in situation where the last recorded move was a downtick. It is a zero tick price in which the last recorded price is higher than the current price. A buy downtick order can be filled and executed only on an downtick or zero-downtick. For such orders, the trade price must always be lower than the last recorded price. This occurs when the execution price is the same as the previous trade, but lower than the most recent trade at a different price. For example, if a series of trades takes place at $25.02, $25.02, and $25.02, the last trade (or tick) is the zero minus tick because it executed at a price equal to that of the previous trade, but lower than the preceding tick of $25.05.

The reverse of a zero downtick (zero minus tick) is a zero uptick (zero plus tick).