The 11th May marks the beginning of Lag BaOmer, a Jewish festival that historically marks a brief reprieve in the Omer, a period of mourning in Judaism.
According to tradition, a long time ago a plague killed thousands of students of the Rabbi Akiva, a significant figure in Judaism. The plague ended on Lag BaOmer, and so this day marks a 24 hour period of celebration in the midst of a time for mourning and remembrance.
On this day couples can get married, and people can generally relax and have fun. In Israel it is customary to plant trees. It’s a respite from the gloom and misery, and a much welcome one.
My understanding of this festival is fairly basic, unfortunately, so if anyone has anything to add or any accounts of their personal experiences with this festival please feel free to comment and share your knowledge with myself and others!