Mains also refers to the central steading of a townland (fermland)

Mains (sometimes just main) refers to the interconnected cables or pipes carrying a service to households and businesses, and to the service they supply. The term is most often used with electricity, gas and water . It is also sometimes used when talking about sewage services. The name is not used with data and telecoms services which generally have a dedicated link for each customer.

Generally when referring to the system itself the name of the service is placed before the word main or mains (e.g. "he dug up the water main") whilst when referring to the service the word mains is placed first or omitted entirely (e.g. "my laptop is currently running on mains electricity" or "my drill runs off the mains").

Mains services (especially electricity and water) are considered very desirable features for a home or business property. Water and sewage services were essential in cleaning up towns and electricity has allowed for things that were otherwise impossible, inconvenient or dangerous. Whilst electricity generation and to a lesser extent water extraction and sewage disposal are all possible to do locally, centralising them can bring big benefits in quality, cleanliness and efficiency.

Mains services are natural monopolies and therefore governments (either local or national) are usually heavily involved in their provision. This may be either through government ownership or heavy regulation.

A special type of mains are traction power networks for the supply of electric trains with traction current used in Germany, Austria, Switzerland and some areas around New York.