A cookie sheet is a flat, rectangular baking pan used primarily for baking cookies. It typically has low sides or no sides at all, allowing for easy access to the cookies and promoting even baking. Cookie sheets are usually made from materials like aluminum, stainless steel, or non-stick coated metal, which help distribute heat evenly. These sheets come in various sizes, with standard dimensions being around 13 by 18 inches. Some cookie sheets may have a raised edge, known as a rimmed baking sheet, which can be useful for other baked goods like brownies or roasted vegetables. Proper care and maintenance can extend the life of a cookie sheet.