A
substance that is a poor
conductor of
electricity. In other words, it has a high
resistance to the flow of
electrons. Part of the
conductor,
semiconductor, insulator
troika.
Printed-circuit boards must be good insulators for fairly obvious reasons. Insulators are commonly seen on telephone poles. The biggest are seen hanging from the arms of high-tension or high-voltage towers, where they keep the current going through the wires from leaking through the tower to ground.