Tinfoil/ˈtɪnfɔɪl/ Definition 1 of 3Pro Tip 1/3Kitchen Essential Tinfoil is commonly used for cooking or preserving food's freshness and taste. My mom always uses tinfoil to cover lasagna while baking. Pro Tip 2/3Heat Reflection Tinfoil reflects heat, so it's often used to keep food warm. Cover the roasted chicken with tinfoil to keep it warm. Pro Tip 3/3Avoid Contamination Use tinfoil to wrap food and prevent it from contact with other items. She wrapped her sandwich in tinfoil for the picnic.