Frozen ground
Soil or rock in which part or all of the pore water is frozen (Van Everdingen, 1998). Frozen ground includes permafrost. Ground that freezes and thaws annually is called seasonally frozen ground.
Definition courtesy of IPCC AR4.
All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.