From: An Introduction to Jewish Calendar
by Menachem Persoff

Purim in a Nutshell

Purpose

Purim celebrates the events narrated in the Book of Esther, which
took place in the middle of the 5th century BCE. Purim specifically
commemorates the deliverance of the Jews in Persia from the hands of Haman,
the king's officer, who plotted their death.

Date: 14th Adar.

Shushan Purim

The 15th Adar is known as Shushan Purim since in the Persian capital of Shushan,
the Jews were required to continue defending themselves against their enemies
for one more day.

Name

The name Purim is derived from the word pur meaning "lot." It refers
to the evil machinations of Haman who cast lots to determine on which day he
should arrange for the slaughter of the Jews of Persia.

Observance

In the Synagogue

On the eve of Purim and on Purim morning, Megillat Esther
- the Book of Esther - is chanted to a special melody. At the mention of
Haman the children stamp their feet or turn their "greggers" (sort of
rattles) in derision of the name of the arch enemy.

In the Home

Purim is the occasion for parties and celebrations and a
festive meal or seu'dah which is held with family and friends. People give
charity and exchange gifts of food, as required by the Book of Esther.

Because of the turnabout of the fate of the Jews, there is also a custom of
masquerading on Purim, including masked parades and carnivals in Israel.