Medium-textured matzo meal is about the same texture as cornmeal. It is used for baking, as a coating for fried foods, to thicken, and to make matzo balls from.
Fine-textured matzo meal is more finely ground for use in cakes. It is labelled cake meal.
Coarse matzo meal is called “matzo farfel.”
Finely-ground unsalted crackers, particularly unsalted soda-crackers. In the UK, you can use Water Biscuits. Just whiz them up in a blender or food-processor. Or, dried finely-ground breadcrumbs.
1 cup matzo meal = 3 matzos
Matzo Meal was first sold commercially, already ground and ready to use, by the Manischewitz Company in the early 1900s.