Purim [Hebrew:פורים] is an annual festival of the Jews in commemoration of the preservation, as recorded in the Book of Esther, of their people from threatened wholesale massacre in Persia at the insistence of Haman, and which was so called because it was by casting "lots" that the day was fixed for the execution of the purpose. It is celebrated in most of the world on the 14th of Adar, in walled cities from the time of Joshua, it is celebrated on the 15th. It is the most joyous of Jewish festivals. 
Laws and customs
- The megillah must be heard twice once in the evening (night of the 13th of Adar), and once in the morning.
- Charity must be given to at least two paupers (מתנות לאביונים).
- Gifts of at least two ready to eat food items to at least one friend (משלוח מנות)
- A festive meal (סעודה) must be eaten on the day of Purim.
- It is a custom to drink until "one does not know the difference between Haman and Mordecai (עד דלא ידע).
- It is a custom among many to dress up in a costume, to celebrate the happiness of the day.
- It is customary to make noise when the name of Haman is mentioned.