The term all-or-none (AON) refers to an instruction which can be added to orders placed with securities brokers by investors. When you place an all-or-none order with a securities broker, the broker will only buy or sell the desired securities if they can buy or sell the full amount.
If the order cannot be completed in full, it remains active until the broker can find a suitable counterparty unless it is canceled by the investor.
Using all-or-none orders can help investors avoid paying more fees than necessary. This may be the case, for example, when brokers charge a minimum brokerage fee per transaction, rather than charging brokerage fees on a per-order basis. Because the entire order is filled in just one transaction rather than multiple smaller transactions.