usage
Two distinct flavors: (1) figurative - a hideout where bad people gather (赌博窝子 'gambling den', 黑窝子 'criminal hideout'); (2) literal angling jargon - a 'spot' chummed with bait so fish congregate (打窝子 'to chum a spot'). The second meaning is unfamiliar to most learners but very common among Chinese fishing enthusiasts.