How do you reduce backlog?

You could streamline the process, hire someone else, produce more, work on any specific points where things slow down, or you could prioritize the most important things, and dump the rest. It really depends on what you are talking about and what is most appropriate. A backlog of nice-to-have features for your software might be easily pruned, but a backlog of patients who will die without a heart transplant is a whole other situation, and your approach to backlog will have to be different in different situations. The solution will be different as well, depending on the constraints imposed by your available resources.