Having decided to include the Megillah in the Hagiographa, the Sages decreed that it would be read in public on Purim. It is a mitzvah to eat a copious and festive meal on Purim, including meat dishes and wine. The origin of Se'udat Purim is in the feast organized by Queen Esther and in the manner that the Jews in Persia celebrated the miracle of their deliverance. It is customary to sing Purim songs and parodies at this meal.
The Megillah also cites two further customs - mishlo'ah manot (shelakhmones, sending of gifts to one another) and "matanot la-evyonim" (gifts for the poor), so that we share our joy and our meal with other people. The Purim rejoicing is also expressed in the wearing of disguises and masks to mark the reversal of fate and the fact that Esther concealed her origins. On Purim we dress up, as if to change our appearance and our conduct. The Adloyada is a kind of costume carnival in which we are commanded to drink to intoxication, until we no longer know whether we are blessing Mordechai or cursing Haman.
At the festive meal, and during the rest of the day, we eat hamantashen (Haman's ears). "Tash" means "pocket", but it also means "exhausted", and by way of a joke we can thus say that because of the merits of the three Patriarchs "tash coho shel Haman", Haman's forces were exhausted. It is also customary to make a noise with a rattle, every time Haman's name is mentioned.
JEWISH AND ISRAELI HOLIDAYS:
Reference material for teachers and students in the Diaspora, Edited by Dr. Aviv Ekroni & Rafi Banai From: "Hetz",
Journal of the Department for Jewish Education and Culture in the Diaspora