A trading halt occurs in the U.S. when a stock exchange stops trading on a specific security for a certain time period. The halt, which can happen a few times a day per security if FINRA deems it, usually lasts for one hour, but is not limited to that. Trading halts can happen any time of day. The listed company is supposed to call the exchange where it is listed, 10 minutes prior to any material news that they are releasing, in order for the exchange to halt the stock before the news is released. The first 5 minutes of a halt is for "news pending" before any information is released that could affect a stock significantly, also known as the "5 minute window".[1]

Trading halts usually occur when a publicly traded company is going to release significant news about itself. The halt in trading for the affected security gives investors time to review the news and assess its impact. Another situation in which a trading halt might occur is when the exchange is uncertain "whether the security continues to meet the market’s listing standards." [1]

Note, there are also "trading pauses", which are defined as, under NASDAQ, "if a security is subject to a Trading Pause, the Pause Threshold Price field will contain the reference threshold price that deviates 10% from a print on the Consolidated Tape that is last sale eligible as compared to every print in that security on a rolling five (5) minute basis".