noun
report of absence (from work); absentee notice
A formal written notice submitted to an employer or school to report an absence, typically in advance or as soon as possible. Often a standardized form.
体調が悪いので、会社に欠勤届を提出した。
I submitted a report of absence to my company because I wasn't feeling well.
欠勤届は前日までに出してください。
Please submit your absentee notice by the day before.
Compound of 欠勤 (absence from work) + 届 (report, notice). The okurigana variant 欠勤届け reflects the verb 届ける (to deliver, to report).