A mainline refers to the primary or central pipeline, cable, or conduit that carries a resource, such as electricity, water, gas, or data, to different parts of a system or infrastructure. In electrical systems, the mainline typically refers to the primary power line that distributes electricity from the source (like a power plant or grid) to residential, commercial, or industrial areas. It acts as the main route for power delivery, connecting local transformers, circuits, and electrical panels to the larger grid. Mainlines are crucial for the efficient and stable distribution of energy or services.