Which of the following best describes Romex?

Romex refers specifically to a brand name commonly used to describe indoor nonmetallic electrical cable. It is designed for residential wiring, which can often be found running through walls and ceilings and is characterized by its plastic sheathing that contains multiple conductors. This type of cable is popular because of its ease of installation and flexibility in wiring applications, ensuring safe electrical connections within a structure.

The other choices do not accurately capture the nature of Romex. It does not pertain to a type of roofing material, a brand of roofing nails, or insulation used in roofing systems, making the identification of Romex as an electrical cable the distinct and correct description.