Metallicity refers to the abundance of elements heavier than hydrogen and helium in a star, galaxy, or other astronomical objects. It is an important factor in understanding the formation and evolution of celestial bodies, as higher metallicity often indicates a more complex history of star formation and chemical enrichment. In astronomy, metallicity is usually expressed as a ratio compared to the Sun, which is considered to have a metallicity of zero. This measurement helps astronomers categorize stars and galaxies, providing insights into their age, composition, and the processes that shaped them over time, such as supernovae and stellar nucleosynthesis.