Solstice:
Summer Solstice is the first day of the Season of Summer. On this day June 20th in the Northern Hemisphere, the Sun is the farthest North and the length of time between Sunrise and Sunset is the longest of the year.
Winter Solstice is the fist day of the Season of Winter. On this day December 21th in the Northern Hemisphere the Sun is the farthest South and the length of time between Sunrise and Sunset it the shortest of the year.
Equinox:
There are two Equinoxes every year - in September and March - when the sun shines directly on the Equator and the length of the day and night is nearly equal. 12 hours all over the world. Seasons are opposite on either side of the equator.
Spring Equinox is the first day of the Season of Spring, also known as the Spring (vernal) Equinox. And falls on March 20th.
Autumn Equinox is also known as the Autumnal (fall) Equinox is the first day of the Season of Autumn. The Autumn Equinox occurs the moment the Sun crosses the celestial Equator from North or South. This day is September 22th.