All or none 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

Investment banking

An investment bank is a financial institution that assists individuals, corporations and governments in raising capital by underwriting and/or acting as the client's agent in the issuance of securities...

, an all-or-none clause in an underwriting contract

Underwriting contract

In investment banking, an underwriting contract is a contract between an underwriter and an issuer of securities.The following types of underwriting contracts are most common:...

 or investment prospectus

Prospectus (finance)

In finance, a prospectus is a document that describes a financial security for potential buyers. A prospectus commonly provides investors with material information about mutual funds, stocks, bonds and other investments, such as a description of the company's business, financial statements,...

 gives a securities issuer

Issuer

Issuer is a legal entity that develops, registers and sells securities for the purpose of financing its operations.Issuers may be domestic or foreign governments, corporations or investment trusts...

the right to cancel an issue in its entirety if the underwriting is not fully subscribed.