An order that instructs a broker to sweep the entire book (order book) and then locate the best prices on the market, regardless of offer size (on the other side), and fill the order, either in one go, or piece by piece until the whole order is filled and executed. An order that does the same across multiple markets is a special case of a sweep order: an intermarket sweep order (ISO) is an order (limit order) that sweeps the market place, usually using an algorithm, identifying as many securities as possible at the best prices available.

This type of orders is especially used by option traders who require speedy filling of orders over the best possible price.