Parity vs Parity bit vs Parity sum
I don't think the term has a clear standard accepted meaning, so if you are reading it somewhere, you'll either have to infer from context or hope they defined the term.  But as a general guideline, I would guess your former choice is much more likely than your second choice; I think it's much more likely to be a single bit than a bitstring.

If you are thinking of using that term in your own writing, I encourage you to define that term before using it.