The term 'Primary Pipes' refers to the main pipes that are used in plumbing systems. These pipes are typically made of metal or plastic and are used to transport water, gas, and other liquids from one place to another. The term 'Mains' is a five-letter word that is often used to refer to these primary pipes. Mains are usually the largest pipes in a plumbing system and are responsible for carrying the most amount of liquid.