All Or None - AON
A condition used on a buy or sell order to instruct the broker to fill the order completely or not at all.
Investopedia Commentary
For example, if you send a AON order to your broker requesting 200 shares at $15, the broker will not fill the order unless s/he can get you the 200 shares at $15. This prevents you from having orders half filled before they expire.
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See also: Fill or Kill, Limit Order, Market Order, Order
Also spelled: AON