An iron–nickel alloy or nickel–iron alloy, abbreviated FeNi or NiFe, is a group of alloys that mostly consist of the elements nickel (Ni) and iron (Fe). It is the main constituent of the "iron" planetary cores and "iron" meteorite. The acronym NiFe is used to refer to various chemical reactions that involve an iron–nickel catalyst or component, or in geology, to refer to the general composition of planetary cores (including Earth's).