nøkkelmasse
Nøkkelmasse is a Norwegian term that literally means key mass or core mass. It is not a term with a single, universally accepted definition in science or engineering; its meaning is highly dependent on context and it appears more often in informal or niche discussions than in formal textbooks.
In mechanical engineering or physics, some writers use nøkkelmasse to denote the principal or defining mass
Etymology: the word is formed from nøkkel (key) and masse (mass). In Norwegian-language sources, compound terms