I'm looking for a concise term to describe something.
Suppose I'm making a gizmo which has application-specific circuitry but also requires substantial computing power. Not wanting to reinvent the wheel, I decide to incorporate a pre-made board, call it PCB "B", which is a single-board computer like an Udoo x86 or Raspberry Pi, for said computing power.
I design a larger PCB, call it PCB "A", which has "B" attach as a mezzanine board via pin headers, stand-offs, etc. PCB "A" has the application-specific circuits and maybe other stuff such as a power supply, connectors to the outside world, etc.
What exactly do you call PCB "A"?
Once upon a time, the physical relationship of "A" and "B" would have qualified "A" as a motherboard. Problem is, since the ubiquity of PCs, that term now carries specific connotations; in particular, it would tend to imply the CPU and computer chipset are on "A" when really they're on "B".
Mainboard has the same problem, as it's generally understood as a synonym of motherboard.
Backplane is not really applicable either, because "A" is not just a bus interconnection board.
Various SBCs have their own terms like shield or cape to describe daughter cards, but while "A" may use some of the same pin headers, using these terms to describe "A" seems to misrepresent it as being diminutive to "B".
Is there some generally understood term for PCB "A" that doesn't carry the wrong connotation?
(For lack of anything better I might call it the "application board", but I prefer to use standard terminology where possible.)