Lag Ba'Omer is a Jewish holiday that falls between the holidays of Passover and Shavuot. This Year Israelis will celebrate Lag Ba'Omer on April 27, 2013. 

"Lag" is a combination of two Hebrew letters Lamed and Gimmel. According to Hebrew numerology, lamed stands for the number thirty and gimmel stands for the number three. This is significant because the holiday is 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 first 32 days of the Omer are observed as a period of mourning in remembrance of Rabbi Akiva's 24,000 students who died, according to the Talmud, in an epidemic during the same period. All restrictions of mourning are lifted on this 33rd day of the Omer. As a result, weddings, parties, music, and haircuts are commonly scheduled to coincide with this day. Many families go on picnics and outings. The most well-known custom is the lighting of huge bonfires throughout Israel and worldwide.

Lag ba-Omer is also connected with the story of the Bar Kochba Revolt, whose spiritual leader was Rabbi Akiva, and whose military leader was Shimon ben Kosiba (Bar Kochba). In the 2nd century CE, some of the Jewish population of Israel revolted against the Roman regime. The revolt, although initially successful, was brutally quashed and wrought great destruction on the Jewish communities in Israel. There is some conjecture that Lag Ba'Omer marks the temporary victory of Bar Kochba’s men over the Romans. 

 

Celebrations in honor of Rabbi Shimon bar Yochai (Rashbi) – Commemorating Rabbi Shimon bar Yochai, who was one of Rabbi Akiva’s students. This is a custom that developed among the kabbalists of Safed in the 16th century and has become a popular folk celebration: on Lag ba-Omer thousands of people have adopted the custom of making a pilgrimage to Rashbi’s tomb in the Galilee, lighting bonfires there in the evening and picnicking throughout the following day. Many religious Jews also bring their three-year-old sons there on Lag ba-Omer for their first haircut.

Bonfires - Lag ba-Omer has become the bonfire holiday, perhaps in commemoration of the signal fires the rebels lit on the mountaintops to relay messages. For weeks before Lag ba-Omer children gather any scrap wood they can find, and on the eve of this holiday large bonfires are lit and potatoes and onions are roasted. Among secular Jews, the bonfires are the only custom that has remained from the traditions of Lag ba-Omer.