equation of the equinoxes (EE)

the right ascension of the mean equinox referred to the true equator and equinox; alternatively the difference between apparent sidereal time and mean sidereal time (GAST − GMST).

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

Original Source: IAU 2006 NFA Glossary