An OCO order links two pending orders — typically a buy stop above the current price and a sell stop below it — so that when one executes, the other is automatically canceled. It's commonly used to trade a breakout in either direction without knowing in advance which way the price will move.
OCO orders remove the need to manually cancel the unused order once the market has already committed to a direction, which matters when a fast breakout leaves no time to react.
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Guide
Order Types and Slippage Explained
Market, limit and stop orders trade price certainty against execution certainty — plus what slippage is, where it comes from, and what a stop-loss caps.