Lag Ba’omer, the 33rd day of the counting of the Omer (18th day of Iyar), is the major exception to the semi-mourning during the Sefira period.

According to Talmudic and midrashic sources (Yev. 62b), during the period between Passover and Shavuot, 24,000 disciples of Rabbi Akiva died of a terrible plague, which miraculously ceased on Lag Ba’omer.

Plague allusion

The “plague” may refer to the overwhelming defeat suffered by the forces of Bar Kochba, whom Rabbi Akiva strongly supported in the unsuccessful rebellion against the Romans. Tradition suggests that the termination of the plague on Lag Ba’omer may be an allusion to the brief recapture of Jerusalem that is said to have occurred on this date.
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