Currency neutrality means that the growth of money supply will lead to the proportional increase of price level.

It has no effect on the actual output level.

Money is essentially a contract between the owner and the market about the exchange of rights, and it is basically an agreement between the owners. I gave all my things to the market in exchange for what I needed. Money is the agreement of this process, which embodies the economic cooperation between individuals and society. The contractual nature of money determines that money can have different forms of expression, such as universal equivalent, precious metal money, paper money, electronic money and so on. It can be used as transaction medium, storage value and accounting unit. Physical currency is a special commodity that acts as an equivalent in the exchange of goods and services, and it is a material appendage and symbol appendage of people's commodity value. It includes not only currency in circulation, especially legal tender, but also various savings deposits. In the modern economic field, only a small part of the currency field is displayed in the form of physical currency, that is, practical paper money or coins, and most transactions use checks or electronic money. Currency area refers to a country or region that circulates and uses a single currency. It is necessary to introduce the concept of exchange rate when different currency areas exchange currencies with each other. In modern economy, money plays a fundamental role. In macroeconomics, money refers not only to cash, but also to cash plus some form of assets.