Pain au chocolat is a French viennoiserie roll made with a combination of rectangular, yeast-leavened dough and a few chocolate sticks or chocolate ganache. The filled dough is rolled, baked, then served, ideally while still hot or warm. This flaky pastry can be bought at numerous French bakeries and supermarkets.
Interestingly, another name for pain au chocolat is chocolatine, and it is mostly used in the southwest of the country. In Bordeaux, there is even a case where customers had to pay more if they ordered a pain au chocolat rather than a chocolatine.