An all-or-none order is:
A condition used on a buy or sell order to instruct the broker to fill the order completely or not at all. If there is insufficient supply to meet the quantity requested by the order then it is canceled at the close of the market.
For example, if you wanted to purchase 15,000 shares of Microsoft at $25 per share “all or nothing,” the stock broker would have to locate all 15,000 shares at $20 in order to complete your requested transaction. If the stock broker could provide 7500 shares at $25 and 7500 at $25.05, then the order would be cancelled at the end of the day.
The order is also commonly known as “All or None.”