Litha is the Wiccan and Pagan Sabbat of the summer solstice (around 21 June), the longest day, when the sun stands at the peak of its strength; it is one of the eight festivals of the Wheel of the Year. Practitioners honour the sun at its zenith even as they mark that, from this height, the days will now shorten toward winter; in the Wiccan myth-cycle it is often read as the height of the sun-god's power before his decline. Customs include lighting bonfires, keeping vigil for the dawn, gathering herbs held to be most potent now, feasting, and celebrating out of doors. Midsummer has genuinely been marked across Europe with fire and festivity for centuries, and modern Pagans draw on that broad tradition.
The name "Litha", however, is a modern adoption rather than an old festival-name. It is taken from Bede, who records Litha as an Old English name for the midsummer months, but there is no evidence it was ever the name of a solstice festival; it was chosen for the neopagan Sabbat in 1974 by Aidan Kelly, who supplied names for the solstice and equinox festivals that, unlike the Celtic-named cross-quarter days, had none, and it spread through the pagan press. This is a clear and well-documented case of the modern Wheel of the Year being furnished with a suitably archaic vocabulary, and it is worth distinguishing the ancient practice of midsummer fires from the recent name now attached to it.