A chemical element, symbol Na — a soft, silver-white metal. On its own it is dangerous and unstable; drop pure sodium into water and it catches fire. You almost never see it alone. In real life sodium comes joined to something else, and the joining you meet every day is table salt: sodium chloride. Because of that, 'sodium' in ordinary speech usually means the salt part of food. Food labels say 'sodium 480mg'; a doctor says 'cut down on sodium', meaning eat less salty food. You will also meet it in fixed names: sodium bicarbonate (baking soda), sodium lamps (the orange street lights), sodium hydroxide. Note the odd pair — the element is 'sodium' but the symbol is Na, from the Latin word 'natrium'; the two do not match, and that is normal in chemistry.