When a material conducts an electric current there is always a small amount of that electric current lost because the conductor has some internal resistance. That is, the electrons flowing through the conductor “bump into” the atoms and other electrons in the conductor, which generates heat that warms up he conductor. If it gets hot enough it starts to glow too. The part where the electrons “bump into” the atoms and electrons in the conductor is called resistance.
A superconductor is a material that has no internal resistance and the electrons in the electric current flow through the superconducting material without bumping into anything. On Earth this condition can only be created at temperatures well below zero, but the race is on to produce the first room temperature superconductor as this will revolutionise the micro-electronics industry. Neutron stars are not a suitable alternative!