A jungle is a dense, tangled, near-impenetrable tropical rainforest, the sort that is found in pulpy adventure stories (in which case it is full of aggressive jaguars, poisonous snakes, stinging insects, hostile natives, and a thousand other hazards).
In real life, a jungle is not simply a tropical rainforest; it's a disturbed tropical rainforest. Mature (climax stage) tropical rainforests are actually quite open near ground level, as the dense canopy blocks out light, drastically limiting lower plant growth. But when those large canopy trees are removed (either by natural causes such as hurricanes or lightning, or by human activity) a dense thicket springs up, full of plants competing for light. Depending on the region, it may take decades or centuries to return to a canopy-dominated tropical rainforest.
Key characteristics of jungle terrain include near zero visibility, heat and sweltering humidity. Unless you are following a game trail movement is only by cutting your way through the dense undergrowth and is measured in hours per mile rather than miles per hour - miles generally won at the cost of much back-breaking labour with machetes. For best speed the party will relay point duty, giving the other members time to rest and re-sharpen their blades … if only one cutter is available, the rate of movement falls yet again. Of course there is no hope at all of sneaking up on anything that isn't stone deaf like this.
Some scrubbier tropical forest types, found in drier regions than true rainforests, can also have a jungle-like appearance.
Bamboo forest, whilst a completely different biome, has many of the same characteristics whilst rhododendron forest is generally drier and at a higher altitude but similarly painful to negotiate.
If the person talking about "the jungle" seems to be referring to some location in or around a built up area - especially if they happen to be a hobo or other transient - then they're probably talking about a jungle yard instead.
Game and Story Use
- A jungle area can be a good place to hide ruined cities or the like, with the jungle growing up over the old gardens and courtyards and farmlands.
- The "extensive biodiversity" of most jungle environments makes them a great place to catch diseases - from parasites like chiggers and leeches through diseases like malaria and yellow fever carried by stinging insects to simple bacterial and fungal infections that flourish in the slightest wound. Also the constant wet heat softens and degrades skin. Realistically, jungles eat non-natives alive (literally in some cases) without needing to employ apex predators, let alone fantastic creatures. Natives tend to have some inbred resistance, but their lives too are frequently nasty, brutish and short.
- Jungles are also psychologically destructive to non-natives as can be found in many accounts written by those who have been forced to fight in them (the most likely circumstances for an outsider to be forced to go to the jungle and remain there). Realistically, the most normal human reaction to a jungle seems to be to hate the place - only ecologists and jungle natives seem to tolerate the places, and most of them will still prefer to live somewhere else given the chance.
- Jungles also destroy equipment - natural fabrics rot in double quick time, metal rusts at an alarming rate and the pervasive damp gets into electrical equipment that was meant to be waterproof.
- All that said, for the trained survivor jungles are meant to be fairly easy to live in compared to other wildernesses on earth - water is fairly abundant and food can be found if you know what you are looking for and what not to eat. Of course survival is dependant on the rest of the environment not killing you…