I checked the COC and the extended policies Doc, doesn't define it.
What is a borderline vote?
Of course it doesn't. It's up to the mods to let votes that suit their agenda let slip while ones that piss them off and upset enough people to be removed.
So... what does it mean
Judging by the name it's probably a vote that can be counted as a vote but can also be removed. Don't quote me on this though.
Maybe, that seems possible but IDK why they'd make a whole new category considering borderline votes are always deemed sufficient according to the extended policies Doc.
A vote is borderline when it is deeply unclear as to whether it meets the standards. These are votes in the liminal space between clearly permissible and clearly impermissible.
Okay, thank you very much, I can finally live in peace.