It's complicated and related to seasons and the shape of the Earth (Earth is not round in case you didn't know), the Earth's orbit and precession all come into it. It may help to to remember that at the poles during mid winter there is constant darkness and constant daylight during mid summer. At the equator there is little seasonal change in day length. So at points between the equator and the poles the seasonal change in day length becomes more dramatic as you get toward the poles.

As already pointed out there are two times a year when the day length is nominally equal everywhere. The reason for all this strangeness is that the Earth's polar axis (the knitting needle the Earth turns around) is tilted over about 23.5 degrees. As the Earth moves around its orbit the poles alternate in pointing toward the Sun (summer for that pole) and away from the Sun (winter). This gives the seasons and the seasonal change in day length.

Equinox happens when the poles are "side on" to the Sun and is a point in time (an epoch). That means that strictly speaking there can only be one line of longitude where there is an equal day and night time around an equinox.