Slug, or
land slug, is a
common name for any apparently shell-less
terrestrial gastropod mollusc. The word
slug is also often used as part of the common name of any
gastropod mollusc that has no shell, a very reduced shell, or only a small internal shell, particularly
sea slugs and
semislugs (this is in contrast to the common name
snail, which applies to gastropods that have a coiled shell large enough that the animal can fully retract its soft parts into the shell).