These are Hamantaschen.
They are the official cookies of the Jewish holiday Purim.
Marked by costume parties and copious drinking, Purim is a raucous Jewish holiday that celebrates a foiled plot to kill all of the Jews in ancient Persia.
They are named after this guy, Haman.
Haman was one of the Persian king's royal advisers who had it in for the Jews, and especially for a particular Jew named Mordecai. Unfortunately for Haman, the king took a liking to Mordecai's beautiful niece, Esther, and made her his Queen. By wielding her royal influence, Esther convinced the king to save the Jews and kill Haman instead.
Hamantaschen translates to "Haman's pockets" and there are a lot of theories about what they represent — his hat, his ears, his pockets full of evil bribe money.
More importantly, they are triangular cookies traditionally made out of a delicious shortbread dough and filled with fruit preserves, poppy seeds, or marmalade. In celebration of their salvation, Jews eat them during Purim, which is on February 23rd and 24th this year.