Q:
A: do you mean Mishnah Kilayim Matzah? There are five grains that may not be used during Passover in any form except matzo. Wheat, Barley, Spelt, Rye, and Oats (according to Rashi) (or two-rowed barley according to Rambam's interpretation of Mishnah Kilayim 1:1; Yerushalmi Challah 1:1). Wheat and spelt (biblical spelt is now more correctly identified as emmer wheat) are both in the genus Triticum and anything else in the genus is likewise forbidden. Oat-grain is practically gluten-free and belongs to a different tribe than wheat, spelt, rye and barley. Millet and teff are borderline; it takes a few days for them to rise. Dough made from the five grains is considered to start rising 18 minutes from the time it gets wet; if not put in the oven before then it can no longer become true matzo. Matzo can be ground to form coarse (matzo farfel), medium, or fine matzo meal, used in Jewish cooking and as a substitute for flour in Passover cooking.