The term for leavened food forbidden during Passover is chametz.
In Jewish law, chametz generally refers to products made from one of five grains—wheat, barley, rye, oats, or spelt—that have come into contact with water and been allowed to ferment or rise. During Passover, observant Jews avoid eating, owning, or benefiting from chametz, following commandments in the Torah to remove it from their homes.
Chametz is not simply a synonym for every food that makes dough rise. Yeast itself is not automatically forbidden, and chemical agents such as baking soda do not turn a food into chametz when used with suitable ingredients. The key issue is the fermentation of grain under the relevant rules.
Matzah is the contrasting food: it is unleavened bread prepared quickly so the dough does not ferment. Kitniyot—foods such as rice, corn, and legumes—are another common source of confusion. Some communities avoid them by custom, but they are not the same category as chametz.