What are nucleon? What are their number called?

A nucleon is the collective name for two important subatomic particles: neutrons and protons. A nucleon is one of either of the two types of subatomic particles (neutrons and protons) which are located in the nucleus of atoms.

Their number is called atomic mass number.

The mass number (A), also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus.