- a compound, as NaFeO2, formed when ferric oxide is combined with a more basic metallic oxide.
- the pure iron constituent of ferrous metals, as distinguished from the iron carbides.
- any of a group of ferromagnetic highly resistive ceramic compounds with the formula MFe 2 O 4, where M is usually a metal such as cobalt or zinc
- any of the body-centred cubic allotropes of iron, such as alpha iron, occurring in steel, cast iron, etc
- any of various microscopic grains, probably composed of iron compounds, in certain igneous rocks