Purim is a holiday celebrating an event that happened in the year 365 BCE: The saving of the Jewish people from genocide at the hands of the Persian minister Haman.   
The Book of Esther tells the story of how Haman persuades the Persian king Ahasuerus to issue an edict ordering the murder of all the Jews in the Persian empire. Queen Esther, the king’s Jewish wife, employs moral courage and skillful diplomacy to thwart Haman’s plan. Haman and his aids suffer execution as agitators. Purim commemorates the miracle of the saving of the Jewish people from genocide.  
There are many customs and traditions associated with Purim. Today masquerading in costumes is a tradition that has spread across the world. 
We wish all celebrating Jews “Purim Sameach!”