Black mustard seeds are tiny, pungent, dark seeds from the mustard plant, prized in Indian and other cuisines for their intense flavor, used in tempering (tadka), pickles, curries, and chutneys, offering nutrients, antioxidants, and health benefits like improving heart health, though large amounts need caution. They are smaller and hotter than other mustard seeds, becoming nutty and sweet when fried in oil, a common Indian cooking technique.