Lag Baomer

The 33rd day of the Omer counting is celebrated as a holiday for two reasons:
Between Passover and Shavuot, in the early 2nd century, 25,000 disciples of Rabbi Akiva passed away because they were not respectful enough to each other. On Lag B'Omer, they stopped dying. Also, Rabbi Shimon bar Yochai, author of the Zohar, a principle work of Kabbalah, passed away on this day. Having fulfilled his mission in this world, he asked that the anniversary be celebrated as a happy day. On Lag B'Omer we go out to the parks and fields and gather to demonstrate Jewish unity.