This is what it's been called since before it was introduced to base VP with the Boarded promotions. Primarily, it uses code from JFD's work in the dll, in which it's been named plague.
It has been communicated as status or condition in the past, but never debuff (which is too generic and can refer to more than just a temporary negative promotion). Condition and Status refer any temporary promotion applied for any source. Plague refers specifically to a temporary promotion that is applied to a unit by another unit attacking it.