Geocentric Coordinate Time is a coordinate time standard intended to be used as the independent variable of time for all calculations pertaining to precession, nutation, the Moon, and artificial satellites of the Earth. Wikipedia

Time standard used in astronomy Wikidata

Time standard. Wiktionary (translation)

A coordinate time standard intended to be used as the independent variable of time for all calculations pertaining to precession, nutation, the Moon, and artificial satellites of the Earth, equivalent to the proper time experienced by a clock at rest in a coordinate frame co-moving with the center of the Earth. Wiktionary