Jungle usually refers to a dense forest in a hot climate, such as a tropical rainforest. The word Jungle originates from the Sanskrit word Jangala which means a desert or uncultivated land. The term Jungle is prevalent in many colloquial languages of the Indian subcontinent and generally used to refer a dense tropical forest or a swamp. About 6% of the Earth's land mass is classified as jungle. Jungles are vital to sustaining the ecosystems of the Earth as we know it. About 57% of all species live in jungle environments. The term may still be used in a technical context to describe the forest biome rainforest, a forest characterised by extensive biodiversity and densely tangled undergrowth including young trees, vines and lianas, and herbaceous plants. As a forest biome, "jungles" are present in both equatorial and tropical climatic zones, and are associated with preclimax stages of the rainforest. For this reason, jungle is to be distinguished from tropical rainforest in that the former is a profuse thicket of tropical shrubs, vines, and small trees growing in areas outside the light-blocking canopy of a tropical rainforest. Hence, 'jungle' is often found at the edges of climax rain-forests, where human activity may increase sunlight penetration.
Not all regions called "jungles" would qualify as "rain forests" because many would apply "jungle" to the forests of northern Thailand or southern Guangdong in China: but scientifically, these are "monsoon forests" or "tropical deciduous forests" but not "rain forests".
The term "The Law of the Jungle" is also used in this kind of context, drawn from Rudyard Kipling's The Jungle Book (1894) - though in the society of jungle animals portrayed in that book and obviously meant as a metaphor for human society, that phrase referred to an intricate code of laws which Kipling describes in detail, and not at all to a lawless chaos.
The "Cities in Flight" science fiction series by James Blish depicted spaceborne cities flying through the galaxy, which the writer compared to Hobos or Okies of space. The term "jungle", borrowed from the above Hobo term, is used for an area of space where such flying cities congregate.