CUE stands for clear and unmistakeable evidence. It is also called a Motion for Revision.
CUE claims are filed against VA decisions that were made years ago. Basically, the claim is that the rating decision was wrong on its face and should be set aside. If the claim is successful, benefits are paid by the VA all the way back to when the denied claim was filed.
The proof of a CUE claim is not easy. It is not enough to show that the VA decision was wrong. The veteran is required to show that the regulations and facts which were in the C File at the time of the prior decision could lead only to one conclusion and the VA got the wrong conclusion. The court is very strict about CUE claims and, while these claims do get granted, they are not granted very often.