noun, noun which may take the genitive case particle 'no'
off duty; not on duty
Used for police officers, firefighters, guards, and other shift workers to indicate they are not currently on duty. Often used as a noun or with の to modify another noun.
I'm off duty today, so I'll relax at home.
非番の警官が事件に遭遇した。
An off-duty police officer encountered the incident.
非番 means being off duty, the direct opposite of 当番, which means being on duty.
非番 means being off duty, the direct opposite of 当直, which means being on duty.
Compound of 非 (hi, 'non-') and 番 (ban, 'watch' or 'duty'), literally meaning 'not on duty'.