What is NMWU Non-Metallic Wet Underground (Direct Burial Wire)?

CSA C22.2 No. 48 Certified NMWU Non-Metallic Sheathed Cables - Underground Feeder & Branch Circuit Cable

For exposed or concealed wiring in dry, damp, or wet locations, and in Category 1 and 2 locations, like barns and stables, where not exposed to mechanical injury.
For exposed wiring where subject to the weather.
For direct earth burial with protection, in accordance with C22.1, Canadian Electrical Code Part I.

300 VOLTS / -40 ºC MIN, 60 ºC MAX
CSA-NWMU cables are available as two- or three-conductor cables with a bare grounding conductor. 14AWG to 10 AWG solid and 8 AWG to 4 AWG stranded.
Manufactured using annealed (soft) copper conductors and compressed standing for stranded conductors.
Has heat-resistant thermoplastic polyvinyl chloride (PVC) / Nylon insulation for the phase conductors with sunlight, moisture, and fungus resistance.
Black PVC jacket for sunlight and overall protection
Conductors are white and black (for 2 conductor cables)
Conductors are white, black, and red (for 3 conductor cables)
Flame Rated: FT1

The cables meet or exceed the following requirements:

The maximum allowable conductor temperature is 60°C. The minimum recommended installation temperature is -40°C for two-conductor cables (sizes AWG 14 to AWG 6) and -25°C for all other sizes.
For three conductor cables the minimum recommended installation temperature is -10°C (with suitable handling procedures).
Material should be properly stored above 0°C for 24 hours prior to installation.
The maximum voltage rating for all intended applications is 300 volts.
Always verify that the product and installation is in full compliance with all applicable national and local electrical and building codes.