Magnesium oxide is a chemical compound composed of one atom of magnesium and one atom of oxygen. It is an inorganic salt that is white in color and has a variety of uses, including as a dietary supplement, an antacid, and a fire retardant. It is also used in the production of cement, ceramics, and glass. Magnesium oxide is also known as magnesia, which is derived from the Greek word for magnetite, a mineral containing magnesium oxide.