A mustard seed is a small, round seed that comes from the mustard plant. It is typically yellow or black in color and has a mild, nutty flavor. Mustard seeds are commonly used as a spice in cooking, particularly in Indian, Mediterranean, and Middle Eastern cuisines. They can be ground into a powder or used whole, and are known for their pungent and slightly spicy taste. Mustard seeds are also used to make mustard condiments, such as mustard paste, sauce, or prepared mustard.