Gill is a thin, flat structure found in aquatic animals, primarily fish. It is responsible for extracting oxygen from water, allowing these creatures to breathe. Gills are typically located on either side of a fish's head and are covered by a bony plate called the operculum in many species. In addition to fish, some amphibians and certain invertebrates also possess gills during their life cycles. For example, tadpoles have gills when they are young, which later develop into lungs as they mature into frogs. Gills play a crucial role in the survival of these organisms in their aquatic environments.