Instant Execution vs Market Execution
Brokers & RegulationTwo order-fill models: instant execution fills at the shown price or requotes; market execution always fills, but at the best available price.
Instant execution fills an order at exactly the price displayed, or rejects/requotes it if that price is no longer available — common with dealing-desk and market-maker brokers. Market execution instead fills the order at the best available price at that moment, whatever it is, without a requote — the standard model for ECN and STP brokers.
Market execution avoids the friction of requotes but exposes the trader to slippage in either direction; instant execution avoids slippage but can mean more frequent requotes during volatile periods.