EGM96
EGM96 (Earth Gravitational Model 1996) is a geopotential model of the Earth consisting of spherical harmonic coefficients complete to degree and order 360.
See https://en.wikipedia.org/wiki/EGM96
ODM2 Elevation Datum Controlled Vocabulary
ODM2 Working Group
A vocabulary for describing vertical datums. Vertical datums are used in ODM2 to specify the origin for elevations assocated with SamplingFeatures.