货币供应量有3个定义，分别是M0、M1及M2，但部份地区会定义为M1、M2及M3。

依中央银行现行定义：

在香港，银行分为三类：括持牌银行、有限制牌照银行(RLBs)及接受存款公司(DTCs)。由银行持有的纸币和硬币不是货币（Money），因为不能用作支付用途，不符合货币的定义。

In economics, the money supply or money stock, is the total amount of monetary assets available in an economy at a specific time. There are several ways to define "money," but standard measures usually include currency in circulation and demand deposits (depositors' easily accessed assets on the books of financial institutions).