The term which describes different atomic masses of similar atom because of varying numbers of neutrons are Isotopes.
Explanation:
The isotopes are the chemical element which has different atomic masses due to the fact that number of neutrons are not same but it has same number of proton.
When the number of neutron increases in a nucleus, with the same electronic configuration and same number of proton, element is said to have isotopes. There are may be variants of isotopes of an element. For example, hydrogen has 3 isotopes.