GMT, Greenwich Mean Time, Greenwich Time, universal time, UT, UT1 - the local time at the 0 meridian passing through Greenwich, England; it is the same everywhere

Earth-received time, ERT - the coordinated universal time when an event is received on Earth

transmission time, TRM - the coordinated universal time time when a transmission is sent from Earth to a spacecraft or other celestial body

SCET, spacecraft event time - the coordinated universal time time on board the spacecraft; "SCET = TRM + OWLT"