The traditional unleavened bread eaten during Passover is known as matzah, matzo or matza; this is a hard, yeast-free flat bread made from flours of specific grains, including rye, wheat, spelt, oat and barley. Though matzah is known as unleavened bread, some diners will find that it has a taste and consistency that is much closer to that of a cracker than bread. Matzah is hard, crispy and crumbly rather than soft and chewy like fresh, untoasted leavened bread.
The "unleavened" aspect of matzah is the most symbolically and ritualistically essential part of this Passover food. People who observe this holiday cannot consume or use any leavening agents such as yeast during Passover. This is symbolically significant because, in the story of Passover, the Hebrew slaves who were finally able to escape from Egypt didn't have time to let their bread rise before they baked it, resulting in flat bread. Matzah's flat form can also be said to symbolize humility.
Machine-made matzah is typically square-shaped, but matzah can be made into any shape. Round is a traditional option, and it is typically an indication that the flatbread was made by hand. Matzah that is used as part of a seder should be made only with flour and water.