The metallicity distribution function is an important concept in stellar and galactic evolution.
It is a curve of what proportion of stars have a particular metallicity ([Fe/H], the relative abundance of iron and hydrogen) of a population of stars such as in a cluster or galaxy.
[1][2][3][4][5][6][7] MDFs are used to test different theories of galactic evolution.
Much of the iron in a star will have come from earlier type Ia supernovae.
Other [alpha] metals can be produced in core collapse supernovae.