Lag BaOmer (Hebrew: ל״ג בעומר‎), is a  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 biblical mandate to count the Omer appears in Leviticus 23:15–6, which states that it is a mitzvah to count seven complete weeks from the day after Passover night ending with the festival of Shavuot on the fiftieth day. The 49 days of the Omer correspond both to the time between physical emancipation from Egypt and the spiritual liberation of the giving of the Torah at the foot of Mount Sinai on Shavuot, as well as the time between the barley harvest and the wheat harvest in ancient Israel. There are a number of explanations for why the 33rd day is treated as a special holiday.