The name for the equinox that occurs on March 20th or 21st of each year is the "Spring Equinox" in the Northern Hemisphere and the "Autumnal Equinox" in the Southern Hemisphere.
During the Spring Equinox, the day and night are almost equal in length, and it marks the first official day of spring in the Northern Hemisphere.
Meanwhile, the Autumnal Equinox marks the first day of fall in the Southern Hemisphere, while day and night are also almost equal in length.
These equinoxes occur as a result of the Earth's tilt on its axis, which causes the amount of sunlight each hemisphere receives to vary throughout the year.