I've come across the term "scrub drag" in several papers recently, but can't find a detailed definition of this phenomenon. This is specifically in reference to aircraft and seems to apply to engine positioning.
For example: "Coe observes that scrub drag in cruise could be reduced by pylon mounting the engine over the wing", from the first paper below.
The term is assumed to be known to the reader in the following papers:
The same term in the context of automotive design does not appear to apply.