The phrase "soda pop" is an informal term used to refer to carbonated soft drinks, also known as "soft drinks" or "CSDs." The term is derived from the use of soda ash (sodium carbonate) as a leavening agent in early soft drinks, which produced a fizzy or "pop" sensation in the drinker's mouth. The phrase is commonly used in American English, while other regions may use terms such as "fizzy drinks" or "bubble drinks."