Other forms: matzoth; matzos
Matzo is a cracker-like bread that's traditionally eaten during Passover. When matzo is ground into a flour, it can be used to make matzo balls for soup.
During the Jewish holiday of Passover, observant Jews don't eat anything that's leavened, like yeast bread that rises before being baked. Matzo is a good, if crispy, substitute for bread, and it's unleavened. Matzo is also symbolic, representing both freedom and humility. It's sometimes spelled matzoh or matzah, from the Hebrew matztzah, "unleavened bread," or literally, "juiceless."