At present, the concept of "mass" in science has undergone an undesirable evolution in favor of the prevailing theories of the XX century. In relativistic mechanics, this concept has become a calculated physical quantity and has lost its material content. In quantum mechanics, "mass" is stucking of the elementary particles in the Higgs field. The true phenomenological concept of "mass" is the number of corpuscles of dark (negative) matter in a body, or in an elementary particle. "Mass" is another synonym for dark (negative) matter.