Leavened describes bread or baked goods that have been made to rise using a leavening agent like yeast, baking powder, or baking soda. When you add yeast to bread dough and let it sit in a warm place, the yeast produces tiny bubbles of gas that make the dough puff up and become light and airy. That's what it means to leaven something.

Think about the difference between a fluffy sandwich loaf and a flat cracker or tortilla. The sandwich bread is leavened: it's full of tiny air pockets that make it soft and springy. The cracker is unleavened: it stays flat and dense because nothing made it rise.

In everyday cooking, most breads, cakes, muffins, and pancakes are leavened. Without leavening agents, your birthday cake would be as hard and flat as a brick instead of the soft, fluffy treat you expect.