World Humanist Day is a Humanist holiday celebrated annually around the world on the June solstice, which usually falls on June 21. According to Humanists International, the day is a way of spreading awareness of Humanism as a philosophical life stance and means to effect change in the world. It is also seen as a time for Humanists to gather socially and promote the positive values of Humanism.

The manner in which World Humanist Day is celebrated varies considerably among local Humanist groups, reflecting the individuality and non-dogmatism of Humanism as a whole. Whilst the event might be a simple gathering, such as a dinner or picnic, with ample time for both socializing and reflection, the method of celebration is down to the individual Humanists. Some groups actually develop intricate social rituals, music, and proceedings which highlight the metaphoric symbolism of the solstice and the light (knowledge) which brings us out of darkness (ignorance).

From Wikipedia

Visit Humanists International’s World Humanist Day page for more on the origins and ways to celebrate.