Minus Tick

Designates a trade that occurs at a lower price than the immediately preceding trade. Also referred to as "downtick" or "zero minus tick".

Brokerage firms require that short sell orders follow the "tick test", which means that if a stock is trading at a minus tick price (lower than the previous sale), a short sale at that time is not allowed. Generally, short sales are only allowed to occur on an uptick. This rule helps prevent traders from destabilizing a stock's price by short selling on minus ticks.