Purim (“lots”), described in the biblical Book of Esther, marks the salvation of ancient Persian Jews from a plot to wipe them out. The story transpired in Shushan, the walled capital city of Persia, where, according to the scroll, the plot was only fully foiled on the 15th day of Adar. The scroll describes how Esther, a Jewish orphan, became queen to King Ahasuerus, and was thus in a position to foil the schemes of Haman, the evil vizier who planned the genocide. She was alerted to the plot by Mordechai, her uncle, was evidently on the king’s council.  

The name of the holiday reflects the Pur – the lots drawn by Haman to determine when exactly his (ultimately unsuccessful) plot to destroy the Jewish people was to be carried out.