A stop loss, or SL, is an instruction intended to close all or part of a position when a specified adverse price condition is reached. It turns an exit plan into an order rule, but does not guarantee a maximum loss.
Triggering is different from filling
A stop for a long position is commonly placed below the current market; a short position commonly uses a stop above it. A trailing or adjusted stop can also protect an existing gain. Where available, the trigger reference may be last, mark or index price.
After triggering, a stop-market order seeks execution at available prices and can suffer slippage. A stop-limit order imposes a price constraint, but may remain unfilled if the market moves beyond that constraint.
Position protection has limits
A stop based on last price may not trigger before a liquidation process based on mark price. Gaps, insufficient liquidity and order restrictions can also affect execution. Exit quantity and linked-order behavior matter when a position changes or only part is closed.
Fees and funding affect the final result. The configured stop level is therefore an instruction threshold, not a promised execution price or guaranteed account protection.