Gutter oil, trench oil, or sewer oil (Chinese: 地沟油 / 地溝油; pinyin: dìgōu yóu, or 餿水油; sōushuǐ yóu) is a Chinese slang term for recycled oil. It can be used to describe the illicit practice of restaurants reusing cooking oil that has already been cooked with longer than safety codes permit. It can also be used to describe the reprocessing of rancid yellow grease collected from sources such as restaurant fryers and slaughterhouse waste, or putrified brown grease from grease traps and sewer fatbergs.