Bitcoin is a digital asset designed by its inventor, Satoshi Nakamoto, to work as a currency. It is commonly referred to with terms like digital currency, digital cash, virtual currency, electronic currency, or cryptocurrency.The question whether bitcoin is a currency or not is still disputed. Bitcoins have three useful qualities in a currency, according to The Economist in January 2015: they are "hard to earn, limited in supply and easy to verify". Economists define money as a store of value, a medium of exchange, and a unit of account and agree that bitcoin has some way to go to meet all these criteria. It does best as a medium of exchange; as of February2015 the number of merchants accepting bitcoin had passed 100,000. As of March 2014, the bitcoin market suffered from volatility, limiting the ability of bitcoin to act as a stable store of value, and retailers accepting bitcoin use other currencies as their principal unit of account.