Acronym Finder at http://www.acronymfinder.com/ lists 5 meanings. To me, the one most likely for most of us would be Documents of Understanding, but Data Objects Unprocessed seems relevant if a bit more obscure. While I’d never come across DOU before, it is very similar to the MOU (Memoranda of Understanding) and MOA (Memoranda of Agreement) my government agency employer uses to document the conditions on exchange of data.

If you are referring to RPG, DOU means “Do Until”. This command will perform a loop (matched with an “End” or “Enddo”).
Eg.
X=1
DOU X=5

If you are referring to RPG, DOU means “Do Until”. This command will perform a loop (matched with an “End” or “Enddo”).
Eg.
Eval X=1
DOU X=5
Eval X=X=1
EndDo
This example will go through the loop 5 times with the result of X being 5.
“DOU” is similar to “DOW” (Do While), where the difference is that the DOU will always perform 1 pass through the loop whereas DOW will perform the comparison and only continue into the loop if the condition is met, otherwise the program continues after the End (EndDo).
Eg.
Eval X=1
DOW X=5
X=X+1
Enddo
The result is that the loop will not execute and the value of X is 1.

Document of Understanding is what I have heard it used for.