In astronomy, the solstice is the observation of the Sun of when it appears to no longer be traversing the sky but rather holds steady and then changes direction. The Sun then starts to either either get higher in the sky or starts to get lower. The term comes from the Latin sol (sun) and sistere (to stand still).
The summer solstice is the longest day of the year and is the day the sun reaches the highest position in the sky (for that specific time of the day) that year
The winter solstice is the shortest day and the lowest point the sun gets to (for that specific time of the day) that year.
In the Northern hemisphere, north of the Tropic of Cancer (23.44° north of the Equator) the summer solstice occurs around the 21 June and the winter solstice around 21 December. Summer and Winter Solstices are reversed south of the Tropic of Capricorn (23.44° south of the Equator).
Within the Tropics (between latitudes 23.44° north and south of the Equator) the sun reaches the zenith (directly overhead or 90 degrees from the horizon) twice a year making the determination of a solstice more difficult.
Wikipedia notes that an Analemma is “the observed position of the Sun in the sky when plotted or photographed at the same time every day, or every few days, for a year, the points trace out the analemma (a figure eight)