What is money?

From dictionary, money is a current medium of exchange in the form of coins and banknotes. However, money is no longer in form of coins and banknotes. Bitcoin is another type of money that with different concepts behind it. With a general concept, money is anything in any form that could be used as a medium of exchange. To be used as a medium of exchange, it has several characters. Firstly, only inflation can affect the money's future value. Secondly, it is easy to carry and transfer. Thirdly, its supply is limited but infinite. Anything which have all these three characters could be used as money.