How could a great year be explained in laymen's terms?
According to the definition in NASA's Aerospace Dictionary it is a complete cycle of the equinoxes around the ecliptic that completes in 26000 years:
(NASA SP-7, 1965) The period of one complete cycle of the equinoxes around the ecliptic, about 25,800 years. Also called platonic year. See precession of the equinoxes.
Does this mean that every X years the March 21st and September 22nd will be in a different part of the zodiac and it will take 26000 years to make a full circle?