A specialized order by a customer instructing a broker to initiate execution only at the opening price of the trading day. The order specifies that the security (e.g., a stock) is to be bought or sold only at the opening of the exchange, or as close to the opening as practically possible.

It may also be an order to buy or sell a security at the best price available when the market opens for trading on a given day.

Such an order my be used by investors to secure a position in a security at the opening of a trading session.