A cookie sheet is a flat, rectangular baking pan used primarily for baking cookies. Typically made of metal, it has low sides or no sides at all, allowing for easy access to the baked goods. The smooth surface helps distribute heat evenly, ensuring that cookies bake uniformly. Cookie sheets come in various sizes and materials, including non-stick and insulated options. They are often used not only for cookies but also for roasting vegetables and baking other treats. Proper care, such as avoiding high heat and using parchment paper, can extend the life of a cookie sheet.