Sale that takes place at the same price as the previous sale, but at a lower price than the last different price. Antithesis of zero-plus tick.
Zero Minus Tick
A trade on a security that occurs at the same price as the security's previous trade, which was itself less than the price on the trade before that. For example, a security that trades for $5 at 10:00, $4.90 at 10:01, and $4.90 at 10:02 has experienced as zero-minus tick. Until 2007, a short sale was not permitted on a zero minus tick. See also: Tick test.
The sale of a security when the price is the same as the security's preceding sale price but is below the last different sale price. A short sale of a security is not permitted on a zero-minus tick.