Arborio rice is a variety of short-grained rice used primarily in the classical preparation of risotto.
Short, fat and slightly oval-shaped, arborio rice has a pearly white exterior. There are various size designations, of which superfino, the largest grain size, is the one most commonly used.
Because it undergoes less milling than ordinary long-grained rice, it retains more of its natural starch content. Cooking releases this starch, giving risotto its creamy consistency. A pound of arborio rice can absorb up to 6 cups of liquid without becoming mushy. This process of releasing is starch is key to risotto's creaminess, and it's a process that only happens if it's cooked slowly, with the liquid added a little bit at a time. If you were to prepare arborio rice via the traditional method for cooking white rice, where all the water and all the rice are combined in a pot and then simmered until the water is absorbed, you'd get cooked rice, but not the same creaminess.