Salt

Common salt is a chemical compound made up of an atom of sodium and an atom of chlorine (chemical formula NaCl). In its natural form, it forms cubic crystals. It is highly soluble in water and makes up the vast majority of salts in seawater. It is produced in industrial quantities by evaporation of sea water or by mining it from existing deposits.
Salt is an essential micronutrient in the human diet, providing it with the sodium it requires for nerve function and as an electrolyte to regulate blood volume. It is used in saline which mimics the salt composition of blood, which in turn is roughly the same salinity as seawater itself.
Modern table salt is now fortified with iodine to prevent cretinism and goiter.
Salt at Wikipedia