Summer Solstice is a celestial event that takes place on June 21 every year and on December 21 on the other side of the world.
Summer Solstice has the longest day and shortest night of the year.
It appears in the novels and is the day when Elena Gilbert returns from the afterlife.
Summer Solstice is seen as a sign of rebirth and goodness and a symbol of how light tramples the darkness as the day is longest and the sun lies in the sky the longest in the whole year. It is the opposite of Winter Solstice.
In the book, Elena Gilbert has been dead for six months and Bonnie and her friends are dealing with a new Old vampire called Klaus.
Bonnie McCullough and Stefan Salvatore fight Klaus without much luck.
Bonnie recalls how Summer Solstice is a day when the line between life and death is thin and she uses her extremely powerful psychic and witchcraftic powers to summon Elena's spirit along with warriors from the town's Civil War to help in the battle.
They succesfully kill Klaus and Elena returns to life.