Yes, mass has mass. It is, therefore, matter. If mass did not have mass, then it is "something" with no mass. That would make it "non-matter" and perhaps it might be energy.
Large number of people
Mass and mass are the same thing.
Somerville MA currently does not have a mass transit system.
The atomic mass number is the mass of the isotope of an element (the sum of number of protons and number of neutrons).