A frog is classified as an amphibian. Amphibians are a group of cold-blooded vertebrates that typically begin their life in water, undergoing metamorphosis to develop into air-breathing adults. Frogs spend part of their lives in aquatic environments as larvae, where they have gills for respiration, and then they undergo metamorphosis to transition to a terrestrial life stage, developing lungs. Amphibians also possess moist skin, which plays a crucial role in respiration and moisture absorption. Frogs are known for their jumping abilities, vocalizations, and complex life cycles, making them a fascinating group within the animal kingdom.