@James_Dixon @sickburnbro @WandererUber @binkle Rest mass (not resting mass) is always implied - the mass of object in it's own relativistic rest frame, m_0.

Early textbooks used to fudge things and talk about relativistic mass to make things look like more familiar Newtonian physics. That's not done any more. There is only a particle's intrinsic rest mass, or just mass.