Stop-loss order
TradingDefinition
A standing order to sell once a stock falls to a specified price. Designed to cap downside on a position, but in fast-moving markets the actual fill price can be much worse than the stop trigger (a "gap down"). For better control, use a stop-limit (which converts to a limit order, not a market order, when triggered).
Example
You bought NVDA at $500 and set a stop-loss at $450 to limit losses to 10%. If NVDA falls overnight to $440, your stop triggers — but it converts to a market order and may fill at $435 or lower in the morning.