Citation:
The atomic mass of oxygen is the weighted average mass of an atom of oxygen, based on the relative abundance of different isotopes. It's approximately 16 atomic mass units (amu).
An isotope is a variant form of an element with a different number of neutrons in its nucleus, leading to a different atomic mass.
Atomic Mass Unit (amu): This is a unit used to express atomic and molecular weights. It's one-twelfth (1/12) the weight of a carbon-12 atom.
Relative Abundance: This refers to how common each isotope of an element is in nature.