Sidereal is from Larin sidus “star” and is used by modern science to describe the time it takes for the Earth to orbit the Sun, which is nearly identical to the tropical or solar year.
In esotericism, the term sidereal year is used to describe a much larger pattern: the movement of the entire solar system (ie. Sol, our sun, our star and its accompanying planets) through space.
"Terrible moments are approaching for this humanity, since our solar system has finished its voyage around the zodiacal belt. This means that the sidereal year is ending. I want all of you to know in a clear and precise manner that as there is a terrestrial year, likewise there is a sidereal year; that as the Earth travels around the Sun, similarly our solar system travels around the zodiacal belt. Just as the terrestrial year has four seasons, namely spring, summer, autumn, and winter, thus the sidereal [solar system] year has four seasons spring (golden age), summer (silver age), autumn (copper age), winter (iron age). The present sidereal [solar system] year is approaching its last degrees in the constellation of the water carrier [Aquarius]; this means that it is finishing. Unquestionably, a great cosmic cataclysm always occurs whenever a sidereal [solar system] year concludes." Closing Speech at the 1975 Gnostic Congress