A jungle is a wilderness of dense overgrowth found on planets. Often in places with a tropical climate.
Without its weather control system, Risa was a geologically unstable jungle with a high amount of precipitation. (DS9: "Let He Who Is Without Sin...")
Carraya IV had a jungle, which was home to the arboreal needle snake. (TNG: "Birthright, Part I", "Birthright, Part II")
Soukara had a large jungle near its Dominion base. In 2374, Worf and Jadzia Dax arranged to meet Lasaran in the jungle. They began to make their way through, until Jadzia was injured in a Jem'Hadar attack. Worf later left Jadzia behind to continue, but changed his mind and returned to her. (DS9: "Change of Heart")
Goralis III had a jungle, which Worf and Ezri Dax crashed into in 2375. Worf later caught an animal in it. (DS9: "Penumbra")