Ester in the Bible.
A Jewish woman, Ester, was raised by her cousin Mordechai.
Ester then became part of the harem of Ahasuerus, the King of Persia. Ahasuerus loved Esther very much and made her queen, not knowing that she was Jewish.
Haman, an advisor to the king, hated Mordechai, who refused to bow down to Haman. Thus Haman plotted to destroy the Jewish people. Haman told the King of the people that "do not observe the King's laws" and Ahasuerus gave Haman permission to do with the Jews as he pleased. Haman chose to have all the Jews killed.
Mordechai persuaded Esther to speak to the King on behalf of all the Jewish people. This was dangerous for Esther, because it meant being in the presence of the King without being summoned, and that could have resulted in her death. Esther fasted for three days and then went to see the King, who welcomed her. Esther told the King of Haman's plans. The Jewish people were saved and Haman was hanged on the gallows that were meant for Mordechai.
The message of the story is that God often works in ways that are not apparent, and that may appear to be chance, coincidence or good luck.
Purim is celebrated on the 14th day of Adar, which is usually in March. Purim means "lots" and refers to the lottery that Haman used to choose the date for the massacre of the Jews. During leap years there are two months of Adar, and Purim then takes place in the second month of Adar.
The Book of Esther is known as the Megillah. During Purim the custom is to hear the reading of the book of Esther. Whenever the name of Haman is mentioned in the reading, people boo, hiss, and stamp their feet.
The Jewish people are required to eat, drink and be merry during this feast. Everyone is required to drink until they cannot tell the difference between "cursed be Haman" and "blessed be Mordechai" - of course without violating other commandments or getting seriously ill from the effects of the alcohol. People are also expected to send out gifts of food and drink and give to charity.