The word "equinox" comes from Latin, where equi means "equal" and nox means "night."
It would be easy to assume that day and night would be of equal length of 12 hours each. However, that is not entirely true.
At the equinox, the measurement is taken from when the centre of the Sun is at the horizon and there are12 hours between sunrise and sunset.
The top edge of the Sun is visible first at sunrise and last at sunset. Due to light refraction, there is still light for a short time even when the sun is no longer visible. This adds a little extra time to daylight hours.
In spring, this means that the date when day and night are actually equal happens before the equinox - known as the equilux which means "equal light".
This year the equilux is on 17 March in the UK.
One thing that is absolutely true is that beyond the equinox, days will be longer than nights, until the summer solstice on 21 June.