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• closed loop
  closed loop

  noun

  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.
• closed-loop
  closed-loop

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

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Example Sentences

See Examples For:

closed loop closed-loop

In a way, all this has been building for a decade in a closed loop of X, podcast and Substack discussions, albeit a closed loop involving millions.

From The Wall Street Journal ● Sep. 15, 2026

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

A closed loop of pressurised water will pass round the reactor, and heat up.

From BBC ● Dec. 4, 2024

Vance is participating in his own closed loop.

From Slate ● Aug. 31, 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

Caterpillar’s giant yellow dump trucks have been running autonomously on closed-loop courses in mines and quarries for several years.

From The Wall Street Journal ● Sep. 19, 2026

But the new facilities increasingly use closed-loop liquid cooling, which continually recirculates coolant instead.

From MarketWatch ● Sep. 18, 2026

"We should simply ban data centres from using potable water supplies. We should require them to use closed-loop systems".

From BBC ● Aug. 29, 2026

Technologies developed for sustaining life on Mars, including desiccation-resistant crops and efficient closed-loop life support systems, could improve sustainability on Earth.

From Science Daily ● Jul. 17, 2026

The company is prioritising renewable energy such as solar panels and closed-loop server cooling systems that continuously recycle water, Nah said.

From Barron's

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