Where does oxide come from?

An oxide is a chemical compound consisting of molecules in which at least one oxygen atom is bonded to other elements. Most of the Earth's crust consists of oxides. Many oxides are produced when elements react with oxygen in the air. Several materials that are considered "pure elements" have an oxide coating.

What does forming oxides mean?

Most of the Earth's crust consists of solid oxides, the result of elements being oxidized by the oxygen in air or in water. Even materials considered pure elements often develop an oxide coating. ... Certain elements can form multiple oxides, differing in the amounts of the element combining with the oxygen.