Purim is celebrated on the 14-15 of Hebrew month Adar. As all Jewish holidays Purim begins in the evening of Adar 14 and ends in the evening of Adar 15.
Purim commemorates the annulment of a decree to kill all the Jews in the Persian empire. The story of Purim is told in the book of Esther of the Tanach.
Esther was the queen of Persian king Ahasuerus who ruled from 486 to 465 BC. The Greek name of king Ahasuerus is Xerxes.