Lag BaOmer falls on the thirty third day of the counting between Pesach and Shavuot, a period otherwise kept with restrictions on celebration, and the day interrupts them. At Meron it is kept as a hillula, a word that means a wedding feast and is used for the anniversary of a sage's death, on the reasoning that a righteous person's death is a union rather than a loss.
The sage is Rabbi Shimon bar Yochai, a second century figure whose tomb is traditionally at Meron and to whom the Zohar is ascribed by kabbalistic tradition. Bonfires are lit and kept through the night, singing and dancing continue until morning, and the upsherin, the first haircut given to a boy of three, is performed in the courtyard. Arthur Green's study of the tzadik as a point of contact between heaven and earth explains the underlying logic of the gathering: the grave of a righteous person is treated as a place where prayer is more likely to be effective, and going there is a devotional act in its own right.
Hasidic and Mizrahi communities are especially strongly represented, for whom veneration of a tzadik at his grave is a central devotional practice, though attendance today runs across the whole range of observance and includes many who keep little else. The day is also marked with bonfires by children across Israel and in Jewish communities elsewhere, well away from Meron, which makes it one of the more visible minor festivals of the year.