Illuminating gas is a term used to describe the gas used in gas lamps to produce light. There are various synonyms for this term, including coal gas, town gas, and gaslight. Coal gas is a type of gas produced by the destructive distillation of coal, while town gas is a similar gas produced from any carbonaceous material, such as coal, oil, or biomass. Gaslight is another term used to describe illuminating gas. The term originated from the gas lamps that were commonly used in the 19th century to provide light in homes and streets. Regardless of the term used, illuminating gas is still occasionally used today in certain applications.