Definitions for "Stock Ahead"
When two or more orders for a stock at a certain price arrive about the same time, and the exchange's priority rules take effect. NYSE rules stipulate that the bid made first should be executed first, or, if two bids come in at once, the bid for the larger number of shares receives priority. The bid that is not executed is then turned to the broker, who informs the customer that the trade was not completed because there was "stock ahead.".
An expression used on the floor of the New York Stock Exchange to signify that one or more brokers had made a prior bid (or offer) at the same price as an order you had entered.
Sometimes an investor who has entered an order to buy or sell a stock at a certain price will see transactions at that price reported on the ticker tape while his own order has not been executed. The reason is that other buy and sell orders at the same price came in to the specialist ahead of his and had priority.