If you retire from the military and later get approved for VA disability compensation, you might expect the two checks to simply add together. For most retirees, that is not how it works. Retired pay and VA disability compensation both come from federal funds set aside to compensate service members, and without an exception, the government will not pay you in full for both.
The rule that reduces one against the other is generally called the VA disability offset, and it catches a lot of new retirees off guard the first time their retired pay drops. Two programs, CRDP and CRSC, exist specifically to restore or replace that reduction for retirees who qualify. Knowing how the offset works, and whether you're exempt from it, matters as much as knowing your disability rating.