What does atomic mass refer to in an atom?

Atomic mass refers to the weighted average mass of an atom's isotopes, measured in atomic mass units (amu). This measurement takes into account the number of protons and neutrons present in the nucleus of an atom. Protons and neutrons, collectively known as nucleons, contribute significantly to the mass of the atom because their mass is much greater than that of electrons, which are negligible in comparison when calculating atomic mass.

As a result, when discussing atomic mass, it is important to recognize that it is determined by adding the number of protons and neutrons together. This cumulative count reflects the actual mass of the atomic nucleus. In essence, the correct understanding of atomic mass emphasizes the importance of both protons and neutrons, since they make up the majority of the atom's mass.