A pump that delivers what it was programmed to deliver, vs. a system that watches the body and decides what to deliver next.
This is fundamentally a control-systems distinction applied to drug dosing, and it maps directly onto the classic open-loop vs. closed-loop control taxonomy. An open-loop drug delivery system — which describes most infusion pumps in clinical use — delivers a fixed, pre-programmed dosing schedule set by a clinician, with no sensor feedback loop adjusting that schedule based on the patient's real-time physiological state. A closed-loop system senses an actual physiological signal — continuously measured glucose, for instance — and an algorithm adjusts dosing in real time based on that measurement, the way an artificial pancreas / automated insulin delivery (AID) system continuously modulates insulin infusion based on continuous glucose monitor (CGM) readings rather than a fixed basal rate alone.