Peroxide is a compound with the structure R-O-O-R. The O−O group in a peroxide is called the peroxide group or peroxo group. In contrast to oxide ions, the oxygen atoms in the peroxide ion have an oxidation state of −1.
The most common peroxide is hydrogen peroxide (H2O2), colloquially known as "peroxide." It is marketed as a solution in water at various concentrations. Since hydrogen peroxide is colorless, so are these solutions. It is mainly used as an oxidant and bleaching agent. Concentrated solutions are potentially dangerous when in contact with organic compounds.
Aside from hydrogen peroxide, some other major classes of peroxides are these: