Mustard seeds are the small round seeds of various mustard plants. The seeds are usually about 1 to 2 millimetres (0.039 to 0.079 in) in diameter and may be colored from yellowish white to black. They are important herbs in many regional foods and may come from one of three different plants: black mustard (Brassica nigra), brown Indian mustard (B. juncea), or white mustard (B. hirta/Sinapis alba).

Mustard seeds have been highly prized culinary oil-seeds being in use since earlier times. The seeds are fruit pods obtained from mustard plant, in the Brassica family. Some of close members of mustards in this family include cabbage, broccoli, brussels-sprouts, etc. Scientific name: Brassica juncea.