The term for a permanent frozen layer of soil is called permafrost. Permafrost is found in polar regions and some high-altitude areas where temperatures remain below freezing for extended periods, typically for at least two consecutive years. This layer can vary in thickness and can influence local ecosystems, as it affects vegetation, drainage, and the availability of nutrients. The presence of permafrost also impacts infrastructure development in these regions, as buildings and roads must be designed to accommodate or mitigate its effects due to potential thawing and instability.