Frog on corn leaf

Frogs are amphibians in the order Anura (meaning "tail-less", from Greek an-, without + oura, tail), formerly referred to as Salientia (Latin salere (salio), "to jump"). Most frogs are characterized by a short body, webbed digits (fingers or toes), protruding eyes and the absence of a tail. Frogs are widely known as exceptional jumpers, and many of the anatomical characteristics of frogs, particularly their long, powerful legs, are adaptations to improve jumping performance. Due to their permeable skin, frogs are often semi-aquatic or inhabit humid areas, but move easily on land. They typically lay their eggs in puddles, ponds or lakes, and their larvae, called tadpoles, have gills and develop in water. Adult frogs follow a carnivorous diet, mostly of arthropods, annelids and gastropods. Frogs are most noticeable by their call, which can be widely heard during the night or day, mainly in their mating season.

The distribution of frogs ranges from tropic to subarctic regions, but most species are found in tropical rainforests. Consisting of more than 5,000 species described, they are among the most diverse groups of vertebrates. However, populations of certain frog species are declining significantly.

Amphibians (class Amphibia, from Amphi- meaning "on both sides" and -bios meaning "life") are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic (or cold-blooded) tetrapods. Most Amphibians undergo metamorphosis from a juvenile water-breathing form to an adult air-breathing form, but some are paedomorphs that retain the juvenile water-breathing form throughout life. Mudpuppies, for example, retain juvenile gills in adulthood. The three modern orders of amphibians are Anura (frogs and toads), Caudata (salamanders and newts), and Gymnophiona (caecilians, limbless amphibians that resemble snakes), and in total they number approximately 6,500 species. Many amphibians lay their eggs in water. Amphibians are superficially similar to reptiles, but reptiles are amniotes, along with mammals and birds. The study of amphibians is called batrachology.

Amphibians are ecological indicators, and in recent decades there has been a dramatic decline in amphibian populations around the globe. Many species are now threatened or extinct.

The earliest amphibians evolved in the Devonian period from lobe-finned fish that used their strong, bony fins to venture onto dry land. They were the top predators in the Carboniferous and Permian periods, but they later faced competition from their descendants, the reptiles, and many lineages were wiped out during the Permian–Triassic extinction. One group, the metoposaurs, remained important predators during the Triassic, but as the world became drier during the Early Jurassic they died out, leaving a handful of relict temnospondyls like Koolasuchus and the modern orders of Lissamphibia.

Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and independently. All animals are also heterotrophs, meaning they must ingest other organisms or their products for sustenance.

Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago.