Pokémon nests in Pokémon GO are designated spawn points that consistently produce a specific Pokémon species for a period of time, typically two weeks, before shifting to another species. The species appearing at a nest changes regularly due to Niantic's migration events. By visiting a known nest location, trainers can significantly increase their chances of encountering and catching multiple of the featured Pokémon, making it an efficient way to gather candies, find high-IV specimens, or even hunt for shiny variants.