Lag B'Omer, the 33rd day of the counting of the days between Pesach and Shavuot, will be celebrated on May 20. The letters lamed and gimmel, which spell the word "lag," have a value of 33. It's a time to light a campfire with your parents and friends, and to make toy bows and arrows (my kids love to make foam-tipped arrows).
Here is a story told about Lag B'Omer: For many weeks, Rabbi Akiva's students were struck by plague. It is said that it happened because they were disrespectful to each other; 24,000 students died. But, on Lag B'Omer, the plague stopped. Rabbi Akiva began to teach his five remaining students. From that day on, the light of Torah began to spread again. This is one reason given for lighting bonfires on Lag B'Omer.