Purim, which commemorates the events described in the Book of Esther, mainly the foiling of the plot by anti-Semitic Haman, Grand Vizier of the Persian Empire, to massacre the Jews, is celebrated in carnivals and costumes.

Excerpt from Government Press Office press release, 5-Mar-2012:

Purim commemorates the events described in the Book of Esther. In Esther 3:8, the anti-Semitic Haman, Grand Vizier of the Persian Empire, tells Persian King Ahasuerus that, “There is a certain people scattered abroad and dispersed among all the peoples... in your kingdom. Their laws are different from those of every people, neither do they keep the king's laws. Therefore, it does the king no profit to suffer them. If it please the king, let it be written that they be destroyed...” Thus, Haman coined one of the most infamous anti-Semitic canards: That the Jews are a clannish and alien people who do not obey the laws of the land. At Haman's contrivance, a decree is then issued for all Jews in the Persian Empire to be massacred. But, as the Book of Esther subsequently relates, Haman’s plot was foiled and, “The Jews had light and gladness, and joy and honor...a feast and a good day.” (8:16-17)

Throughout the centuries, Purim – which celebrates the miraculous salvation of the Jews and the thwarting of Haman’s genocidal plot – has traditionally symbolized the victory of the Jewish people over anti-Semitic tyranny. As such, Purim is a happy, carnival-like holiday.

After sunset Wednesday evening, 7 March, festive prayers will take place in synagogues, where the Book of Esther will also be read aloud. It is customary for people, especially children, to come to synagogue dressed in costume. During the reading of the Book of Esther, whenever Haman’s name is mentioned, congregants traditionally make as much noise as possible in order to drown out his name – a reflection of God’s promise (Exodus 17:14) to, “blot out,” the Amalekite nation, of which Haman was a descendant; special Purim noisemakers may be used for this purpose. The Book of Esther will be read again during morning prayers on Thursday, 8 March. A special Purim prayer is inserted into the daily prayers and the blessing after meals.

On Purim, Jews are enjoined by the Book of Esther (9:22) to send gifts of food to each other, make special contributions to the poor, and have a festive holiday meal in the afternoon. To this end, the day is also marked by collections for various charities, and by people visiting neighbors and friends to deliver baskets of food, prominent among which are small, three-cornered, fruit-filled pastries known as Oznei Haman in Hebrew (Haman’s ears) or Hamantaschen in Yiddish (Haman’s pockets).

In Jerusalem, Purim is ordinarily celebrated one day later than it is in the rest of the world; accordingly, all Purim-related observances are postponed by one day. This practice originates from the fact that an extra day was prescribed for the Jews of Shushan (the modern Susa, one of the Persian Empire's four capitals) to defend themselves against their enemies. This second day is known as Shushan Purim. As mentioned in the Book of Esther itself (9:16-19), Jews living in walled cities (later defined by rabbinical authorities to mean walled cities at the time that Joshua entered the Land of Israel) celebrate Purim one day later than Jews living in unwalled cities. There are several such cities in Israel where Shushan Purim is celebrated. In some cities whose status is in doubt, the Book of Esther will actually be read on both days.