The Viperidae (vipers) are a family of venomous snakes found in most parts of the world, with the exception of Antarctica, Australia, Hawaii, Madagascar, as well as various other isolated islands, and north of the Arctic Circle. All have long (relative to non-vipers), hinged fangs that permit deep penetration and injection of snake venom. Four subfamilies are currently recognized. They are also known as viperids. The name "viper" is derived from the Latin word vipera, -ae, also meaning viper, possibly from vivus ("living") and parere ("to beget"), referring to the trait viviparity (giving live birth) common in vipers, but not in snakes at large.