Any item that is widely acceptable in exchange for goods and services. Fiat money is the medium of exchange in developed economies but over the course of economic history many other items have played this role. Gold is one of the most prominent, and there is evidence that seashells were once a medium of exchange in Bengal. Cigarettes are reputed to be a medium of exchange within the informal economy of prisons. All that is required for a commodity to be a medium of exchange is that it has a significant cost of production and that it is widely acceptable. The manufacturing cost of fiat money may be very low but the state maintains a monopoly and uses security measures to protect its monopoly, thus raising the production cost for parties other than the state. The existence of a medium of exchange allows trade to take place without the need for a coincidence of wants: in the absence of a medium of exchange it is necessary to find a person willing to barter the goods one is selling for the goods one wishes to buy. A medium of exchange facilitates economic transactions.