A cookie sheet is a flat, rectangular baking pan used primarily for baking cookies. It is typically made of metal, such as aluminum or stainless steel, and has low sides or no sides at all. This design allows for even heat distribution and easy access to the cookies during baking. Cookie sheets come in various sizes and may have a non-stick coating to prevent cookies from sticking. They can also be used for other baked goods, such as biscuits or scones, and are often lined with parchment paper for easier cleanup.