What does mass really mean?

Answer 1

A: The amount of matter in an object. A: Physicists are currently trying to find out the "source" of mass, but it is highly unlikely that the answer will be very satisfying to an ordinary person. Perhaps the only way to view this is to accept that mass is that which has the properties which we recognize in Newtonian physics, such as inertia and gravitational attraction, and in Einsteinian physics such as energy equivalency and the bending of spacetime. In other words, mass just is.