shift duty; on-call duty
Refers to working a scheduled shift, often overnight or on weekends, commonly used in hospitals, security, and similar fields.
I have shift duty twice this week.
The doctor on shift duty handled the emergency patient.
当直 is a more general term for being on duty or on call, while 当直勤務 specifically refers to the shift work itself.
夜勤 means night shift, whereas 当直勤務 can include day, night, or weekend shifts depending on the schedule.
Compound of 当直 (とうちょく, 'on duty') and 勤務 (きんむ, 'work, service'). The exact historical derivation is uncertain, but the term is a straightforward combination of these two Sino-Japanese words.