Define "coaxial cable" in terms of its structure.

Coaxial cable is defined structurally as a type of electrical cable that consists of an inner conductor, which is typically made of copper or aluminum, surrounded by an insulating layer. This insulating material serves to separate the inner conductor from an outer conductive shield, which is usually made of braided or solid metal. The outer shield not only protects the inner conductor but also helps prevent electromagnetic interference, allowing for better signal quality over longer distances.

This layered construction is key to the coaxial design, as it enables the cable to carry high-frequency signals effectively and reduces the loss of signal strength. The design also allows coaxial cable to be relatively flexible while maintaining durability, which is essential for both installation and long-term use in various applications, such as television, internet, and telecommunications.

This definition underscores why the other options do not apply. The description of multiple independent wires in a plastic sheath relates to different types of cables, while a simple wire that transmits radio signals lacks the essential structural components that define coaxial cable. Lastly, fiber-optic cables are entirely different in structure and function, utilizing light instead of electrical signals for data transmission.