A zero minus tick is a trade in an exchange listed security that occurs at the same price as the previous transaction, but at a price that is less than the last transaction that was different.
Applying "Zero Minus Tick" to Securities Exams:
If XYZ trades on the NYSE with the trades taking place as follows:
XYZ 3s.24.02… 4s.24.01…..3s.24.01….4s.24.02
The first trade of 300 shares at 24.02 sets the baseline for this example. The next trade of 400 shares at 24.01 is a minus tick since it is a lower price than the previous trade. The second trade of 300 shares at 24.01 is a zero minus tick since its at the same price as the previous trade but at a lower price than the last trade that was different in price. The last trade of 400 shares at 24.02 is a plus tick since it is at a higher price that the previous trade.