Core terms
Trading halt
A temporary stop in trading of a stock, declared by the listing exchange or a regulator, for reasons such as pending news or a volatility pause. Each halt carries a reason code.
Halts differ by cause. Nasdaq's codes include T1 (news pending), T2 (news released), T12 (additional information requested by Nasdaq), LUDP (a limit up–limit down volatility pause) and H10 (an SEC trading suspension). A news halt can last until the company has published the information; a volatility pause usually lasts five minutes and can be extended. An SEC trading suspension can last up to ten trading days.
Small caps on big moves can halt several times in a day. A halt says that trading stopped and why; it does not say which way the stock will reopen. Trading resumes through a reopening auction, and the first price can be far from the last trade before the halt.
What traders should verify
Know how your broker handles orders during a halt: open orders may stay in the queue, be cancelled, or become eligible for the reopening auction. Check the reason code before assuming the cause.
Do not conflate
Halt codes and procedures differ by listing exchange. FennEdge records the halts it receives from exchange feeds; a list on a page may not be every halt of the day.