A toilet seat is a hinged unit consisting of a round or oval open seat, and usually a lid, which is bolted onto the bowl of a toilet used in a sitting position. The seat can be either for a flush toilet or a dry toilet. A toilet seat consists of the seat itself, which may be contoured for the user to sit on, and the lid, which covers the toilet when it is not in use – the lid may be absent in some cases, particularly in public restrooms.

A toilet is a piece of sanitary hardware that collects human urine and feces, and sometimes toilet paper, usually for disposal. Flush toilets use water, while dry or non-flush toilets do not. They can be designed for a sitting position popular in Europe and North America with a toilet seat, with additional considerations for those with disabilities, or for a squatting posture more popular in Asia, known as a squat toilet. In urban areas, flush toilets are usually connected to a sewer system; in isolated areas, to a septic tank. The waste is known as blackwater and the combined effluent, including other sources, is sewage. Dry toilets are connected to a pit, removable container, composting chamber, or other storage and treatment device, including urine diversion with a urine-diverting toilet.