Purim is March 17, 2022, beginning the evening of the 16th. In Jerusalem, Shushan Purim is celebrated on the 18th.
Purim is a joyous holiday commemorating the salvation of the Jews in ancient Persia. Haman the Amalekite receives King Ahasuerus's permission to annihilate the Jews, but the king's Jewish queen Esther, prompted by her cousin Mordechai, intercedes with the king and the decree is turned on its head. The decree is turned on its head, instead allowing the Jews to avenge themselves of their enemies on the very day their destruction was fated. The Jews celebrate their victory on the subsequent day, the 14th of Adar.