what category should this be sold under?

That's going to be a peripheral board.

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thank you probably going to be a dumb question but what can I look for to differ between mother boards and periphial boards?

A motherboard must have multiple external gold pin ports, multiple internal gold pin ports, a CPU (soldered or socketed), north and south bridge chips.
That said there are rare cases where a motherboard is missing one of the above and Still qualifies as a mobo but that's the most basic way to tell.

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