Money

Money is any item or verifiable record that is generally accepted as payment for goods and services and repayment of debts, such as taxes, in a particular country. The main functions of money are distinguished as: a medium of exchange, a unit of account, a store of value and sometimes, a standard of deferred payment. Any item or verifiable record that fulfils these functions can be considered as money.

Definition

According to Principles of Economics by Timothy Taylor (3rd edition),

Money. Whatever serves society in three functions: medium of exchange, unit of account, and store of value.

According to Macroeconomics by Mankiw (7th edition),

Money. The stock of assets used for transactions. (Cf. commodity money, fiat money.)