What is defined as any wire approved for direct underground burial without conduit?

The term that describes any wire approved for direct underground burial without the need for conduit is Direct Burial Wire. This type of wire is specifically designed to withstand the conditions associated with being buried in the ground, such as moisture, soil contact, and varying temperatures. It is insulated in a way that protects it against these environmental factors, making it suitable for underground installations.

The other types of wires mentioned have different applications or requirements. Conduit Wire is not intended for direct burial; it typically requires additional protection provided by conduit. Outdoor Rated Wire, while suitable for outdoor use, may not have the same level of durability or moisture resistance required for underground applications. Submersible Pump Wire is specifically designed for use in water applications, usually for connecting pumps submerged in water, and is not categorized as a direct burial wire. Thus, the definition aligns perfectly with Direct Burial Wire since it is the only option that meets the criteria for installation without conduit protection.