An order to buy minus- that is, it shall be executed only on a “minus” or “zero-minus” tick. This involves 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 zero-minus tick/ zero-downtick. For such orders, the trade price must always be at same level or lower than the last recorded price.

The opposite of a buy minus is a sell plus.