The Christian holiday of Easter (the celebration of the Resurrection) occurs contemporaneously (ooh that word!) with the Jewish holiday of Purim and the Muslim holiday of (I can’t spell it). It also coincides with the Druidic and Egyptian spring fertility ceremonies centered around the vernal equinox. Easter is a moveable feast, one of the few in the Christian calendar that is not on a fixed date. For reason, see above.
Anyway, Easter is always celebrated on the first Sunday after the first full moon after the 21st of March (the vernal equinox). It can therefore fall as early as March 22nd (assuming a full moon on the 21st and Sunday the 22nd) and it can fall as late as the end of April (I’m not going to get into those calculations). In any event, it’s the celebration of the coming of the light, the greening of the earth and (hopefully) the coming of warmer weather.
In Georgia, we also celebrate the coming of Pollen Season, where everything turns bright yellow.