Mustard is a thick yellow or yellow-brown paste with a sharp taste from the ground seeds of mustard plants (white or yellow mustard, Sinapis hirta; brown or Indian mustard, Brassica juncea; or black mustard, Brassica nigra), by mixing them with water, vinegar or other liquids, and adding ingredients such as flour. A strong mustard can cause the eyes to water, burn the palate and inflame the nasal passages.