Amphibians are a class of cold-blooded vertebrate animals known scientifically as class Amphibia. They are characterized by their ability to live both in water and on land, which is reflected in their name derived from the Greek word meaning "double life"

. Key characteristics of amphibians include:

• Ectothermic (cold-blooded) metabolism, relying on external sources to regulate body temperature

• Four limbs (except for limbless caecilians) and vertebrate structure

• Moist, smooth, and permeable skin that allows them to absorb water, oxygen, and sometimes carbon dioxide; this skin also contains glands that produce proteins for defense and other functions

• A life cycle that typically involves metamorphosis from aquatic larvae with gills (such as tadpoles) to air-breathing adults with lungs, although some species bypass or modify this process

• Reproduction usually requires access to water bodies, where eggs are laid and fertilized externally or internally depending on the species

There are three main orders of living amphibians:

• Anura : frogs and toads, tailless with long hind limbs adapted for jumping and swimming

• Urodela (Caudata) : salamanders and newts, with tails and limbs of roughly equal size

• Gymnophiona (Apoda) : caecilians, limbless, wormlike amphibians adapted for burrowing

Amphibians are important ecological indicators due to their permeable skin and complex life cycle, making them sensitive to environmental changes and threats such as pollution, climate change, and disease

. They play vital roles in ecosystems as both predators and prey, and their skin secretions are studied for potential medical applications

. In summary, amphibians are vertebrates that bridge aquatic and terrestrial environments through their unique biology and life cycle, including frogs, toads, salamanders, newts, and caecilians