Definitions of Several Terms Related to Time

Sidereal Referring to a coordinate system fixed with respect to the distant stars.

Synodic Referring to a coordinate system fixed on the Earth. Because the Earth is orbitting the sun, the sun's rotation period, as viewed from the Earth, is different than the sideral rotation period. Synodic is not to be confused with Synoptic. A synoptic chart is a map of the whole Sun in absolute heliographic coordinates, which displays an integrated view of solar features observed during a Carrington rotation.

See also, the US Naval Observatory's Systems of Time page .

Thanks to "Glossary of Solar-Terrestrial Terms".