It is called Solstice. The Solstice occurs twice each year (around June 21 and December 22) as the Sun reaches its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. The seasons of the year are directly connected to both the solstices and the equinoxes. The term solstice can also be used in a broader sense, as the day when this occurs.
The day of the solstice has either the most sunlight of the year (summer solstice) or the least sunlight of the year (winter solstice) for any place other than the equator. Alternative terms, with no ambiguity as to which hemisphere is the context, are June solstice and December solstice, referring to the months of year in which they take place.