Slippage
The difference between the price you expected on an order and the price you actually got.
Markets move between the moment you click and the moment your order reaches the venue. If the price has shifted, your order fills at the new level. That gap is slippage, and it can go either way - negative slippage costs you, positive slippage hands you a slightly better fill.
Slippage grows when liquidity is thin or volatility spikes: major economic releases, central bank announcements, the Sunday open, or the last minutes before a session close. Stop-loss orders are especially exposed, because they turn into market orders the instant they are triggered.
You can reduce it by trading liquid instruments during peak hours, using limit orders where appropriate, and avoiding high-impact news if your strategy does not depend on it. A guaranteed stop-loss removes slippage risk entirely on that order, but brokers charge a premium for it.
Related terms
The gap between the buy and sell price of an instrument - the broker's built-in cost of trading.
A resting order that closes a losing position automatically at a price you set in advance.
A bank or institution that continuously quotes buy and sell prices your broker can route orders to.