Onions are fundamental bulb vegetables belonging to the Allium family, celebrated worldwide as an indispensable aromatic foundation for almost every major cuisine. Characterized by their layered structure and range of sweet, sharp, or pungent flavor profiles, they are transformed through cooking—mellowing into rich, caramelized depth when slowly roasted or sauted, or adding a crisp, snappy bite when served raw in salads and salsas. Beyond their essential culinary presence, onions are packed with vitamin C, B vitamins, dietary fiber, and potent quercetin antioxidants, which together support immune function, reduce inflammation, and promote cardiovascular health.