I have spoke to supply houses who use the term URD for a direct burial type of cable similar to triplex. What is this found under in the NEC and UL Whitebook? Is it USE?

it comes marked USE/URD

Sparky must be in a hurry This question appears often, and is asked quite frequently in the field. I have heard of inspectors not allowing cable assemblies identified as URD, for the reasons you state. The inability to locate any approval in publications, is the general reason.
URD, or underground residential distribution cable, can be USE, underground service entrance cable. When it is service entrance cable it is commonly, 3 conductors of Aluminum XHHW, with one conductor identified.
URD identified distribution cable can be medium voltage cable, in the range of 4.16 KV, to 34.5 KV. Of course this will not be marked as USE.

Thanks. It helps to know what the abbreviations are. I then conclude URD/USE is used for primary and secondary for residential underground, and USE is secondary?

Tim: Only URD for 600 volts or less will be identified as USE.
URD for primary medium voltage will be PE, XLP, EPR, PVC, or CSP.