Purim

Purim (Hebrew:  פּוּרִים (help·info) Pûrîm "lots", from the word pur פור,[3] related to Akkadian pūru) is a Jewish holiday that commemorates the deliverance of the Jewish people in the ancient Persian Empire where a plot had been formed to destroy them. The story is recorded in the Biblical Book of Esther (Megillat Ester מגילת אסתר in Hebrew).

According to the Book of Esther, Haman, royal vizier to King Ahasuerus (presumed to be Xerxes I of Persia), planned to kill all the Jews in the empire, but his plans were foiled by Mordecai and his adopted daughter Esther who had risen to become Queen of Persia. 

The day of deliverance became a day of feasting and rejoicing.

Based on the conclusions of the Scroll of Esther (Esther 9:22):

 "[...] that they should make them days of feasting and gladness, and of sending portions one to another, and gifts to the poor" Purim is therefore celebrated by:

Exchanging reciprocal gifts of food and drink known as mishloach manot.

Donating charity to the poor known as mattanot la-evyonim.

Eating a celebratory meal known as a se'udat Purim'.

Public recitation, usually in synagogue, of the Scroll of Esther known as kriat ha-megillah.

Reciting additions to the daily prayers and the grace after meals known as Al HaNissim.

Other customs include drinking wine, wearing of masks and costumes, and public celebration.

Purim is celebrated annually according to the Hebrew calendar on the 14th day of the Hebrew month of Adar (and on Adar II in Hebrew leap years that take place every 2 to 3 years), the day following the victory of the Jews over their enemies. In cities that were protected by a surrounding wall at the time of the Biblical Joshua, Purim is instead celebrated on the 15th of the month of Adar on what is known as Shushan Purim, since fighting in the walled city of Shushan continued through the 14th day of Adar. 

Today, only Jerusalem celebrates Purim on the 15th of Adar.