It's called an isotope.
For example, in the element hydrogen, it has 3 stable Isotopes. These include the hydrogen atom with no neutrons, 1 neutron, and 2 neutrons. They're still an hydrogen atom, as they still have 1 proton, but they're Isotopes of hydrogen.
Each element has a different number of stable Isotopes, some may get only one, but some may get a lot.
Note that Isotopes is only the different numbers in neutrons, but not proton or electrons.
