What does equinox mean in science?

a) longest day of the year

b) shortest day of the year

c) equal day and night

d) none of these

Equinox means equal days and nights. There are two equinoxes on Earth every year, around March 21 and around September 22. There are also nick names for these equinoxes. Vernal equinox which means spring equinox and autumnal equinox which means fall equinox.