A promissory note is a legal instrument (more particularly, a financial instrument), in which one party (the maker or issuer) promises in writing to pay a determinate sum of money to the other (the payee), either at a fixed or determinable future time or on demand of the payee, under specific terms. If the promissory note is unconditional and readily salable, it is called a negotiable instrument.
Referred to as a note payable in accounting (as distinguished from accounts payable), or commonly as just a “note”, it is internationally defined by the Convention providing a uniform law for bills of exchange and promissory notes, although regional variations exist. A banknote is frequently referred to as a promissory note: a promissory note made by a bank and payable to bearer on demand. Mortgage notes are another prominent example.