the.com/concrete jungle

means A densely built, high-rise city environment seen as harsh, impersonal, and almost a wild ecosystem of its own where survival rules still apply.

from A 20th-century metaphorical coinage pairing 'concrete,' the literal building material of modern cities, with 'jungle,' long used figuratively in English for any dense, lawless, survival-of-the-fittest environment (as in 'law of the jungle'). The phrase caught on through mid-1900s writing about urban poverty and alienation, and was cemented in popular culture by songs and films using it to cast the city as a wilderness with concrete trees and asphalt undergrowth — nature's rules, just rebuilt in steel and cement.