matzah or matzoh meal
Matzo meal is made by grinding matzo, a traditional Jewish unleavened bread. Matzo bread is made by mixing flour and water, rolling it out thin, then baking it in an extrmemely hot oven. It can be soft and pliable, or cracker crisp. It is the crisp version that is used to make matzo meal.
Prepared matzo meal come in several types from course to fine. You can also make your own, either from scratch by making and grinding your own matzo bread, or by crushing packaged matzo to your desired consistency.
Matzo is most familiarly used to make matzo balls. But, like all breadcrumbs, matzo meal acts as a binder, and thus can also be added to casseroles, potato pancakes, and more. You can substitute matzo meal in almost any recipe that calls for breadcrumbs.