closed loop

¹ American  

[klohzd loop] / ˈkloʊzd ˈlup /

noun

1. Computers, Electronics. the complete path followed by a signal as it is fed back from the output of a circuit, device, or system to the input and then back to the output.

2. Engineering.

   1. a processing system in which effluents are recycled, that is, treated and returned for reuse.

   2. an automatic control system operating on a feedback principle.

3. a recursive concept, process, or system in which there is no beginning or end point, but rather the products of one phase become the materials for the next, whose products themselves are the materials for the original phase.

   A circular economy is a closed loop, employing reuse, sharing, and remanufacturing to reduce waste.

4. Also called closed time loop.  (in science fiction) a loop in space-time created by someone or something traveling back in time and setting in motion the events of the very timeline that leads to the time travel event, once again setting off events in the past that ultimately result in their being sent back in time, in an infinite, repeating loop.

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closed-loop ² American  

[klohzd-loop] / ˈkloʊzdˈlup /

adjective

1. Engineering.

   1. of or relating to a processing system in which effluents are recycled, that is, treated and returned for reuse.

   2. of or relating to an automatic control system operating on a feedback principle.

2. of or relating to a recursive concept, process, or system in which there is no beginning or end point, but rather the products of one phase become the materials for the next, whose products themselves are the materials for the original phase.

   Around 75 percent of aluminum is kept out of landfills by closed-loop recycling, where used cans are pressed into ingots and rerolled into new cans, which can one day be recycled themselves.

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Etymology

Origin of closed loop¹

First recorded in 1945–50

Origin of closed-loop²

First recorded in 1950–55

Example Sentences

Over longer periods, ammonia created as a metabolic byproduct of Sporosarcina pasteurii could help enable closed loop agricultural systems and might even play a role in Mars's terraforming efforts.

From Science Daily • Jan. 6, 2026

Warm water is pumped from data racks to heat exchangers in the lake, then the cooled water is sent back inside, in a closed loop.

From BBC • Nov. 15, 2025

This included a data centre in Norway which will "run entirely on renewable power" and is "expected" to use closed loop systems.

From BBC • Oct. 16, 2025

Not much happens, but the people are beautiful and so too are their bikes, rumbling beasts that tribe members ride and ride on that familiar closed loop known as Nowheresville, U.S.A.

From New York Times • Jun. 20, 2024

So, one can regard the pair of particles as a single particle moving on a closed loop in space-time.

From "A Brief History of Time: And Other Essays" by Stephen Hawking