What term is used to describe high-density concentrations beneath the lunar surface?

The term that refers to high-density concentrations beneath the lunar surface is "mascons." These are areas on the Moon where there are significant gravitational anomalies caused by dense material located below the surface. This density leads to a higher gravitational pull in those regions compared to the surrounding areas. Mascons play a crucial role in understanding the Moon's geological history and structure, as their study can reveal information about the composition and distribution of materials beneath the lunar surface.

Other terms like "mare," which refers to the large, dark plains on the Moon formed by ancient volcanic eruptions, or "craters," which are depressions created by impacts from celestial bodies, do not describe the specific underground density characteristics. "Regolith" refers to the layer of loose, fragmented material covering solid bedrock on the Moon's surface and does not pertain to the high-density features found beneath it. This highlights the unique nature of mascons in lunar geology.