Here's why:

* Copper (Cu) is a metal.

* Oxide (O) refers to the presence of oxygen.

Metal oxides are formed when a metal reacts with oxygen. In the case of copper oxide, it can exist in two common forms:

* Copper(I) oxide (Cu₂O): Also known as cuprous oxide, it is a red-brown solid.

* Copper(II) oxide (CuO): Also known as cupric oxide, it is a black solid.

Therefore, copper oxide, in both its forms, is a metal oxide.