Definition of missing mass in English:

missing mass

Pronunciation /ˌmɪsɪŋ ˈmas/

noun

Astronomy Physics
  • The amount by which a measured or calculated mass falls short of an expected or inferred mass; (Astronomy) the discrepancy between the mass of a galactic cluster calculated from the velocities of its component galaxies and the mass of the visible (luminous) stars and gas within it, usually attributed to the presence of dark matter; (also) the difference between the mass there must be in the universe if it is closed and the total mass accounted for by direct observation.

    The existence of missing mass and dark matter is at present hypothetical.

Origin

Late 19th century; earliest use found in American Naturalist. From missing + mass.