Cloud forests are a type of evergreen mountain forest found in tropical areas, where local conditions cause cloud and mist to be frequently in contact with the forest vegetation. One of their most obvious features is an abundance of mosses, ferns, orchids and other epiphytic plants on every tree and rock surface.

The definition of a cloud forest is not straightforward. For the purposes of the Mountain Cloud Forest Initiative and the production of cloud forest maps, the definition produced by the 1993 International Tropical Mountain Cloud Forest (TMCF) Symposium has been used.

"The tropical montane cloud forest is composed of forest ecosystems of distinctive floristic and structural form. It typically occurs as a relatively narrow altitudinal zone where the atmospheric environment is characterised by persistent, frequent or seasonal cloud cover at the vegetation level. Enveloping clouds or wind-driven clouds influence the atmospheric interaction through reduced solar radiation and vapour deficit, canopy wetting, and general suppression of evapotranspiration. The net precipitation (throughfall) in such forests is significantly enhanced (beyond rainfall contribution) through direct canopy interception of cloud water (horizontal precipitation or cloud stripping) and low water use by the vegetation.

In comparison with lower latitude tropical moist forest, the stand characteristics generally include reduced tree stature and increased stem density. Canopy trees usually exhibit gnarled trunks and branches; dense compact crowns; and small, thick and hard (sclerophyll) leaves. TMCF is also characterised by having a high proportion of biomass as epiphytes (bryophytes, lichens and filmy ferns) and a corresponding reduction in woody climbers. Soils are wet and frequently waterlogged and highly organic in the form of humus and peat (histosol). Biodiversity in terms of tree species of herbs, shrubs and epiphytes can be relatively high (considering the small areal extent) when compared with tree species-rich lowland rain forest. Endemism is often very high.

TMCF occurs on a global scale within a wide range of annual and seasonal rainfall regimes (ie 500-10,000 mm/year). There is also significant variation in the altitudinal position of this mountain vegetation belt. For large, inland mountain systems, TMCF may typically be found between 2000-3500m (Andes, Rwenzoris), whereas in coastal and insular mountains this zone may descend to 1000m (Hawai,'i). Under exceptionally humid, marine, equatorial conditions, a TMCF zone may develop on steep, small island mountains at elevations as low as 500m or even lower (Kosrae in Micronesia and Gau in Fiji)."

Hamilton, Juvik, and Scatena (1993)

Cloud forests have been subdivided into lower montane, upper montane and subalpine cloud forest. Further information on these definitions can be found in 'Decision Time for Cloud Forests' .

A wide range of terminology is used to describe cloud forests. The term "cloud forest" or its Spanish equivalents are commonly used in association with montane forests in South and Central America, but is rarely used in Asia, Africa, Caribbean Islands or in the Oceania/Pacific region. In Asia the term 'cloud forest' is best equated to the more commonly described upper montane rainforests, although the terms elfin forest and mossy forest are also used. In Africa Afromontane forest is most commonly used, as well 'Upper montane forest'.

The term 'bosque nublado' is the most frequent denomination in Latin America to describe forest under the strong influence of clouds. 'Bosque de niebla' and 'selva nublada' are also used. In Mexico cloud forests are often called 'Bosque mesófilo de montaña'. In the Andean region the belt of cloud forest on the mountainside is sometimes called 'ceja andina'. In Peru, Bolivia and Argentina the mountain forest zone containing cloud forests is often called 'Yungas'.

The most frequently used term in German literature to describe cloud forest is the term 'Nebelwald', signifying fog forest. The term 'Wolkenwald' is also used as a more direct translation of "cloud forest". Another German term is 'Gebirgs-Nebelwald', which means mountain cloud forest.

These included: mossy forest, elfin forest, montane thicket, dwarf cloud forest, nuboselva, bosque montano nebuloso, selva neblina, bosque nuboso, bosque de ceja, selva nublada, nebelwald, wolkenwald, forêt néphéliphile, forêt de nuage, unmu-rin, bosque anao, foresta nebular, mata nebular, matinha nebular, floresta fe neblina, floresta nuvigena, mata de neblina, matinha de altitude, floresta ombrófila densa montana e/ou alto-montana, floresta de altitude, floresta nublada, and floresta pluvial montana e/ou alto montana.