What is the significance of the word 'listed' in the NEC?

The significance of the word 'listed' in the National Electrical Code (NEC) is that it indicates a product has been tested for safety and compliance by a recognized national authority. This listing means that the product has met specific standards for safety, performance, and reliability as defined by applicable testing protocols. These authorities conduct rigorous evaluations and provide certifications that ensure the product can be safely used in electrical installations, effectively reducing the risks of fire, shock, or other hazards associated with electrical systems.

The other choices do not accurately describe what 'listed' entails within the NEC context, which specifically focuses on safety and compliance standards set forth by recognized testing organizations.