closed loop noun 11forms 1 noun11 •A feedback loop, especially when found in: •A closed-loop transfer function. •An electronic feedback loop. •A PID controller. •A closed ecological system. •An economy in which materials are consistently reused rather than discharged as waste. •A path whose initial point is equal to its terminal point. •Closed-loop communication. •Clipping of closed time loop. •The process of pulling water from one area of a reef aquarium and pumping it immediately elsewhere in the tank to create higher flow and minimize dead spots. •Alternative form of knot loop. formsclosed loops