All or none (AON) is a term used most notably in financial transactions in investment banking or securities transactions.
In securities transactions, AON is an attribute attached to a buy or sell order to indicate that the transaction has to be executed in its entirety, i.e. the specified number of shares have to be filled and no partial execution is acceptable. AON does not automatically cancel an order if it cannot be filled as designated, but could be executed without the AON requirement.
In investment banking, an all-or-none clause in an underwriting contract or investment prospectus gives a securities issuer the right to cancel an issue in its entirety if the underwriting is not fully subscribed.