permafrost

American  

[pur-muh-frawst, -frost] / ˈpɜr məˌfrɔst, -ˌfrɒst /

noun

1. (in Arctic or subarctic regions) perennially frozen subsoil.

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permafrost British  

/ ˈpɜːməˌfrɒst /

noun

1. ground that is permanently frozen, often to great depths, the surface sometimes thawing in the summer

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permafrost Scientific  

/ pûr′mə-frôst′ /

1. A layer of soil or bedrock that has been continuously frozen for at least two years and as long as tens of thousands of years. Permafrost can reach depths of up to 1,524 m (4,999 ft). It is found throughout most of the polar regions and underlies about one fifth of the Earth's land surface.

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Etymology

Origin of permafrost

First recorded in 1943; perma(nent) + frost

Explanation

Permafrost is ground that is frozen permanently. As you can imagine, permafrost is extremely cold. If you know that frost has many cold-related meanings and permanent means "always," then you should be able to figure out what permafrost is: ground that is permanently frozen. You won't be able to plant a garden in permafrost — or do much with it — since it’s so hard and cold. You won't find permafrost in warm climates or places that have distinct seasons. Permafrost only exists in areas where it's cold all the time, so the ground never thaws out.

Example Sentences

It also protected what's known as the periglacial environment, which includes things like permafrost - water trapped in frozen soil.

From BBC • Apr. 10, 2026

Managing heat from a data center built on permafrost requires specialized engineering.

From The Wall Street Journal • Feb. 12, 2026

These RNA sequences are the oldest ever recovered and come from mammoth tissue preserved in the Siberian permafrost for nearly 40,000 years.

From Science Daily • Nov. 15, 2025

Canada and Russia, where large amounts of ice and permafrost are melting, are losing the most fresh water.

From Los Angeles Times • Sep. 3, 2025

How could the permafrost have given way like that?

From "Two Degrees" by Alan Gratz