What is the term used for the day on 23 September when day and night are equal throughout the world?

Equinoxes occurs twice in a year. The day and night on this day are equal through out the globe as the Sun is exactly above the equator on this day. This phenomenon occuring on 21 March is Spring equinox and other occuring on 23 September is Autumnal Equinox as the Sun is heading towards Tropic of Capricorn.