Metals
From Slackerpedia Galactica
Astronomers, just to be different, consider anything that isn't hydrogen or helium to be a metal. For some reason the rest of the science disciplines have let astronomy persist with this delusion despite the fact that they outnumber astronomers and therefore could kick their *****.
Astronomers describe certain stars as being metal-poor, what this actually means is that the star consists almost entirely of hydrogen and helium. Metal-rich stars contain other elements besides the hydrogen and helium.
In their quest to be ridiculously terse and incomprehensible astronomers also refer to the percentage of hydrogen as X, the percentage of helium Y and the percentage of metals Z.
Supernovae create lots of metals and distribute them throughout space. As stars form in these environments, they pick up some of this metal. Therefore metallicity in stars can be used to roughly figure out when a star was born.
Ironically, there are no stars in the rock band, Metallica.
