It is very likely it stands for duplicate. If you have lost your driver’s license, or if it was stolen, you’ll need to apply for a duplicate license in person at the DMV.
Losing your driver's license, or or worse yet having it stolen, creates a myriad of problems, but it does happen. Many states require you to file a police report if your driver's license has been lost or stolen or if you know someone is using someone else's driver license numbers.
Do a quick search of DMV's state-specific lost license pages to find answers to all your questions in detail.
To find more information on how to obtain a driver’s license, see the status of your license, check your driver’s license number, order a driving record, and more, visit their Driver's License FAQs page.