A security trade execution order in which the first bid or offer price is executed before other bid and offer prices. Priority executions are undertaken regardless of the volume of the order, meaning that a larger order that does not get to be executed first based solely on its size. Market rules often require the first trade received to be executed first. If two bids or offers are received at the same time, the bid or offer at the larger volume is given priority and is executed first. In this case, the smaller bid or offer is rejected, and the broker placing the bid is told that the rejection occurred because there was a stock ahead.