Lampreys /ˈlæmpreɪz/ (sometimes inaccurately called lamprey eels) are a group of jawless fish composing the order Petromyzontiformes /ˌpɛtroʊmɪˈzɒntɪfɔːrmiːz/, sole order in the class Petromyzontida. The adult lamprey is characterized by a toothed, funnel-like sucking mouth. The common name "lamprey" is probably derived from Latin lampetra, which may mean "stone licker" (lambere "to lick" + petra "stone"), though the etymology is uncertain. "Lamprey" is sometimes seen for the plural form.
About 38 extant species of lampreys are known, with around seven known extinct species. They are classified in three families—two small families in the Southern Hemisphere (Geotriidae, Mordaciidae) and one large family in the Northern Hemisphere (Petromyzontidae).