A solstice is an astronomical event that happens twice each year when the Sun reaches its highest position in the sky as seen from the North or South Pole. The word solstice is derived from the Latin sol (sun) and sistere (to stand still), because at the solstices, the Sun stands still in declination; that is, the seasonal movement of the Sun's path (as seen from Earth) comes to a stop before reversing direction. The solstices, together with the equinoxes, are connected with the seasons. In many cultures the solstices mark either the beginning or the midpoint of winter and summer.

The term solstice can also be used in a broader sense, as the date (day) when this occurs. The day of the solstice is either the "longest day of the year" (in summer) or the "shortest day of the year" (in winter) for any place on Earth, because the length of time between sunrise and sunset on that day is the yearly maximum or minimum for that place.