Closed loop or closed-loop may refer to:
Mathematics
- Loop (topology), a path whose initial point is equal to its terminal point
- Closed curve, a mathematical curve described as a set of continuous parametric equations over a closed interval of real numbers for which the start point equals the end point
Technology
- A feedback loop, often found in:
- Closed-loop transfer function, where a closed-loop controller may be used
- Electronic feedback loops in electronic circuits
- PID controller, a commonly used closed-loop controller
- Closed ecological system not relying on matter exchange outside of the system, as opposed to open loop
- Closed-loop communication, a communication technique used to avoid misunderstandings
- Ecological sanitation systems or ecosan, intended to close the nutrient and water cycle
- 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
Other uses
- Circular economy, one in which materials are consistently reused rather than discharged as waste
- Closed time loop, or predestination paradox, a paradox of time travel that is often used as a convention in science fiction
- Knot loop, a structure used to tie knots