On/off duty Definition 1 of 2Pro Tip 1/3Professional Responsibility Indicates readiness to perform job-related tasks or respond to work matters. The security guard remained on duty throughout the night. Pro Tip 2/3Expected Presence Suggests that someone should be present at a specific place for their work. The nurse on duty was in the hospital ward. Pro Tip 3/3Active Engagement Describes someone currently involved in work activities or operations. The lifeguard on duty promptly jumped in to save the swimmer.