FOK, or "Fill or Kill," is a type of order used in trading that instructs brokers to execute a transaction immediately and completely. If the entire order cannot be filled at once, it is canceled. This ensures that traders can avoid partial fills, which may not meet their strategic goals. FOK orders are commonly used in financial markets, including stock exchanges and cryptocurrency platforms. Traders often prefer FOK orders when they want to ensure that they either get the full amount of shares or assets they desire or none at all, minimizing uncertainty in their trading strategy.