Simply put, a superconductor is a material that electricity can flow through without losing energy along the way. It’s a material with no resistance, it doesn’t diminish an electric current as the current passes through it. The microscopic structure of a superconductor is like an open highway, letting electrons travel through the material with ease.
That means they can conduct electricity more efficiently than any other material. Imagine, electricity buzzing along superconducting wires without losing any energy to But these materials don’t just get their powers from their particular microscopic structure. They also have to be really, really cold-- many hundreds of negative degrees celsius.
If we could use superconductors in electronics, those devices would theoretically run at perfect or near perfect efficiency--they would output the same amount of energy that’s put into them. That would be super useful, you can imagine, when trying to get electricity into your home. In the US we lose about 5-6% of our electricity every year during transmission from the grid to your house because of issues like resistance.