 Metallicity distribution function

The metallicity distribution function (MDF) is a statistical description of the metallicity, which refers to the abundance of elements heavier than hydrogen and helium in a celestial object, such as stars or galaxies. Metallicity is often expressed in terms of the logarithmic ratio of the abundance of a given element to that of hydrogen, relative to the solar abundance, commonly denoted as [Fe/H] (for iron) or other similar indices.