These are tiny round hard seeds which can be black, brown or white and are derived from different plants. The black seeds are extremely pungent and as they are difficult to harvest they are fairly expensive. Even though the white seeds are milder they can still have a fieriness similar to the black seeds. The white seeds are more pungent than the brown ones.
Mustard seeds are high in magnesium, and they are known to help lower blood pressure. The seeds also possess properties which help you to digest food more effectively.
Black or brown mustard seeds are widely used in Indian cooking, especially in south Indian and Bengali cooking. When cooking with them they are added at the start of the dish and fried until they being to pop and release their unique peppery flavour and add a nutty taste to the dish. You can also use them to make various spice blends too.