Snails are neither reptiles nor amphibians. They belong to a class of animals called mollusks, which are characterized by their soft bodies and usually a hard shell. More specifically, snails are gastropods, a large group within mollusks that also includes slugs.
Reptiles, like snakes and lizards, are air-breathing animals that have scaly skin and lay eggs with shells. They are part of the class Reptilia. Amphibians, such as frogs and salamanders, typically start their life in water and then undergo a metamorphosis to become terrestrial adults. They have moist skin and are part of the class Amphibia.
So, while snails share some traits with these groups—such as the ability to live in moist environments—they are fundamentally different, being classified under the Mollusca phylum instead.