When you build electrical circuits, you want to use the BEST CONDUCTOR to make the wires, so you won't lose too much energy in the wires.
The best conductor is Silver. But when you see what it costs, your heart sinks. You begin to think that maybe you can get along without the #1 BEST conductor; maybe the #2 best conductor will work.
The #2 best conductor is copper. People almost always make do with #2.