The term obverse, an its opposite, reverse, describe the two sides of units of currency and many other kinds of two-sided objects, most often in reference to coins, but also to flags (see Flag terminology), medals, drawings, old master prints and other works of art. The terms may respectively be interchanged with the more casual but less precise terms "front" and "back," or (for coins only) "heads" and "tails." In many such areas other than coins, reverse is much more commonly used than obverse, and front and reverse may also be used.