Meaning of “the mains” - Learner’s Dictionary

the mains

noun [ group ] uk /meɪnz/ UK

the system of pipes or wires that carries gas, water, or electricity to a building:

The house isn't connected to the mains yet.

the place inside a building where you can connect a machine to a supply of electricity:

Is the cooker turned off at the mains?

(Definition of “the mains” from the Cambridge Learner’s Dictionary © Cambridge University Press)