Purim is a Jewish festival commemorating the survival of a community of Jews in the 5th century under Persian rule.
One of the most common ways of celebrating this holiday is reading from the Book of Esther, exchanging gifts, and making donations to charities. The three-cornered pastry called "hamantash" (plural: "hamantaschen") is associated with this holiday. Haman was the advisor of the Persian ruler at the time who opposed Mordecai in the Book of Esther. Due to the celebratory nature of this holiday, costumes and parades are associated with Purim.
Because this is a holiday determined by the Hebrew calendar, the official date changes annually between the beginning and ending dates of March. This year, Purim begins on sundown of March 23rd and ends at sundown on March 24th.