This was the idea of P.W. Bridgman, Nobel Prize in Physics for 1946. It was that a concept in science was defined by the way one measured it. If one thinks of electron spin, or the curvature of space, these are not everyday ideas. In everyday life, electrons are not seen, and neither is space seen to be curved. They rest on the results of experiments which measured fundamental properties like time, light, mass, electrical charge, and so on. What Bridgman meant is that their meaning is in the way the measurements were done.