The word mustard is used to refer to several species of plants. These plants belong to the genera "Brassica" or "Sinapis". They have tiny seeds. These seeds can be used as a condiment. When they are first ground, and then mixed with water, vinegar and other ingredients, a condiment called mustard can be made. The seeds can also be pressed, to give a kind of oil called "mustard oil". Some kinds of mustard plants have edible leaves. These leaves are known as "mustard greens".