noun
absence permission slip
A formal document submitted to a school or workplace to obtain official permission for an absence, often for a legitimate reason such as illness or a family event.
公欠届を提出すれば、その日の欠席は公欠として扱われます。
If you submit an absence permission slip, your absence that day will be treated as an excused absence.
欠席届 is a general notice of absence, while 公欠届 specifically requests official permission for the absence to be recognized as excused.
Compound of 公欠 (official absence) and 届 (notification, report).