The one cancels other order option allows you to place a pair of orders stipulating that if one order is executed fully or partially, then the other is automatically canceled. An OCO order combines a stop order with a limit order. This option allows you to place both take profit and stop loss targets for your position (only for limit orders).
Example: If the market price is 250 and the trader wants a stop order at 245 and a limit order at 260, then a OCO order may be appropriate. If the market reaches 245, the stop order will trigger a market order and cancel the limit order at 260. If the market reaches 260 before 245, the limit order will execute and cancel the stop order at 245.
Note: If you manually cancel one of the OCO orders; i.e., the stop or the limit, you must also manually cancel the other one. An OCO order is only automatically canceled if the other order is partially or fully executed by market price movement.