Shmura matzo is a special kind of matzo that meets a higher standard of kosher for Passover rules. The flour used in shmura matzo is supervised from the field to the factory to ensure that it does not come in contact with water that could begin the leavening process. Grains that have come in contact with water and may have become leavened, called hametz, are not allowed to be eaten on Passover. Shmura matzo is usually handmade in a round shape, although there are also some machine-made square shmura matzos available. Shmura matzo costs more than regular machine-made matzo. Some people partake in the custom of eating only shmura matzo throughout the holiday, while some partake in the custom of using only shmura matzo for the Seders.