This is the number of protons and neutrons in the nucleus of any atom.

Mass number

Explanation:

Usually two numbers are used to identify an atom of an element:

- Atomic number: usually represented with Z, it corresponds to the number of protons inside the nucleus of the atom

- Mass number: usually represented with A, it corresponds to the number of protons+neutrons inside the nucleus

Therefore, the correct term for

the number of protons and neutrons in the nucleus of any atom.

is

mass number