All Or None
When an investor puts an All Or None (AON) order, they are giving the broker the following instructions: either fill the whole order or none at all.
In other words, the trader is asking not to allow for any partial fills of the order.
Let us have a simple example to help you understand the mechanism of this order. An investor wants to buy 300 shares of Amazon at 200 USD, which means he wants this order to be filled only if all the 300 shares are priced at 200 USD.
Now the last point that remains to clarify is why inventors choose this order. AON orders are particularly useful for thinly-traded securities.