Lag B'Omer (Hebrew: ל״ג בעומר), is a minor, festive holiday celebrated on the thirty-third day of the Counting of the Omer, which occurs on the 18th day of the Hebrew month of Iyar. (The numerical value of the Hebrew letter lamed is 30, and the value of gimel is three; lamed and gimel together are pronounced “lahg.”) Lag B'Omer gives us a break from the semi-mourning restrictions (no parties or events with music, no weddings, no haircuts) that are customarily in place for some Jewish communities during the Omer.
The Omer has both agricultural and spiritual significance: it marks both the spring cycle of planting and harvest, and the Israelites’ journey out of slavery in Egypt (Passover) and toward receiving the Torah at Mount Sinai (Shavuot). An omer (“sheaf”) is an ancient Hebrew measure of grain. Biblical law forbade any use of the new barley crop until after an omer was brought as an offering to the Temple in Jerusalem. The Book of Leviticus (23:15-16) also commanded: “And from the day on which you bring the offering…you shall count off seven weeks. They must be complete.” This commandment led to the practice of the S’firat HaOmer, or the 49 days of the "Counting of the Omer,” which begins on the second day of Passover and ends with the celebration of Shavuot on the 50th day.
There are not many traditional Lag B'Omer foods, but in Israel, typical foods eaten on the holiday include kebabs (roasted skewered meat or vegetables), pitas, eggplant salad, potato salad, tehini, etc. Any foods that would go well at a picnic or bonfire are great options for Lag B'Omer.
Lag B'Omer commemorates a variety of historical events, including the end of a plague that killed many students of Rabbi Akiva (c. 50-135 C.E.), the yahrzeit of 2nd-century mystical scholar Shimon bar Yochai, and a Jewish military victory over Roman forces in 66 C.E. In remembrance of these events, some people celebrate with picnics and bonfires. Many Jewish couples choose to get married on Lag B'Omer, and many people also choose to wait until that day to get a haircut or beard trim.