Lag BaOmer is not mentioned in the Torah and only hinted at in the Talmud. Consequently, there is no formal ritual associated with the holiday. Rather a series of attractive and meaningful Lag BaOmer rituals have evolved over time.
Lag BaOmer is a shorthand way of saying the 33rd day of the omer. In addition to tracking the agricultural cycle, the omer marks the period from Passover, which commemorates our people’s exodus from Egypt, to Shavuot, which commemorates the giving of the Torah at Mount Sinai.
The journey from Egypt to Sinai was not only biblical, but spiritual as well. As the Israelites hiked through the desert, they also had to find their way through the wilderness of their souls, preparing themselves not only to be given the Torah, but to accept the Torah.
Historically, the period of the Omer is a time of semi-mourning, when weddings and other festivities are avoided, in memory of a plague that killed thousands of students of Rabbi Akiva, a Talmudic scholar. Lag BaOmer was the day on which the plague ceased, and thus became a day on which the mourning rituals are abandoned and are replaced with great joy.