When we think of money, we usually think of currency, or metal coins and paper bills. In the modern world, almost every country and every person uses coins and paper money to exchange for other objects of value. The sizes and shapes of coins are different in various countries, and the size and color of paper money also vary. In India, for example, some coins have square sides. In japan, some coins have holes in the centre. In the United States, all paper money is the same size and the same color; only printing on the bills is different. Most other countries have various sizes and colors for different values of paper money.