Solstice refers specifically to summer solstice and winter solstice. The summertime solstice has the greatest amount of sunlight that day of the year, while the winter solstice is the day when there is the least amount of sun. The summer solstice typically falls on June 21st. This time, the Northern Hemisphere leans toward the sun, and the southern hemisphere is going away from the sun.
Winter solstice typically falls on December 22nd and is when the sun is at its furthest point from the equator. Equinox is the sun at its nearest point from the equator. During the equinox, the cusp between day and night time rests at a 90-degree angle at the equator.
The autumn equinox occurs on September 22nd, while the spring equinox happens on March 20th. Autumn is the cooling down of summer as you prepare for the cold, dark winter, while spring is the heating up after the harsh winter, and it prepares you for the hot and humid days of summer.