ELI5: Explain Like I'm 5

Double-circuit transmission line

A double-circuit transmission line is like two highways side-by-side. Each highway, or circuit, can carry electricity (or other energy like heat) over long distances. This is useful when you need to transfer a lot of energy very quickly, like when you need to power a whole city. The two circuits working together makes it stronger and more reliable so that it can transport even more energy than just one circuit.