Final answer:
An insulator does not easily allow electricity to pass through, due to tightly bound electrons and ions. Glass and dry table salt are examples of insulators. Contrarily, conductors like metals allow electric charges to flow freely, facilitated by free electrons or ions.
Step-by-step explanation:
A substance that does not easily transmit electricity is called an insulator. Insulators have their electrons and ions bound tightly within the structure, preventing these charge carriers from moving freely. This property significantly hinders the flow of electric current through the material, making them the opposite of conductors. Examples of insulators include glass, pure water, and dry table salt. In contrast, substances such as metals and salty water contain free electrons or ions that can move relatively easily, classifying them as conductors.
Conductors permit the flow of electric charges through the movement of free electrons or ions, which allows electricity to pass through them readily. On the other hand, superconductors are special cases of conductors that can allow the movement of charge without any energy loss whatsoever.