Baklava is a layered pastry made of paper-thin sheets of phyllo dough brushed with melted butter or oil, filled with chopped nuts (commonly walnuts or pistachios), baked until golden, and then soaked in a sweet syrup - typically a sugar or honey syrup, sometimes scented with rose water or orange blossom water.
Baklava's exact origins are disputed and claimed by several cuisines; it's documented in the Ottoman court by the 15th century and is widely eaten today across the Middle East, Greece, Turkey, and the Balkans, with regional differences in nuts and flavoring - walnuts and cinnamon are more typical in Greece, pistachios and rose water in Turkey. It's a popular dessert for holidays and celebrations, including Eid al-Fitr and Orthodox Christmas.