Acronyms can be confusing, especial acronyms which have many meanings – the popular ones not being what we are looking for. The last time I checked, Wikipedia didn’t have an entry for RDL or “redistribution layer” that fits our industry.
As a simple explanation, a redistribution layer (RDL) is a set of traces built up on a wafer’s active surface to re-route the bond pads. This is done to increase the spacing between each interconnection. This build up is a wafer-level packaging step, a way of doing some of the device packaging before die singulation. This saves money and makes processing quicker and easier. If you are interested in this topic, I recommend checking out this article:
Redistribution Layers by George A. Riley, PhD (FlipChips Dot Com)