Greenwich Sidereal Time (GST)

Greenwich apparent sidereal time (GAST), the hour angle of the true equinox from the Terrestrial Intermediate Origin (TIO) meridian (Greenwich or International meridian).

Source: IERS Technical Note 36: Glossary (PDF, 244KB, Not barrier-free file.) of the IERS Conventions (2010)

Original Source: IAU 2006 NFA Glossary