An automatic pause in trading when prices move too far too fast.
US single stocks pause for five minutes under “limit up–limit down” rules when they leave a price band. Market-wide circuit breakers halt all trading for 15 minutes if the S&P 500 falls 7% or 13% before 3:25 p.m., and close the market for the day at 20%. European exchanges use similar “volatility interruptions” followed by an auction.