The term worm (pronounced /ˈwɜrm/) refers to an obsolete taxon (vermes), currently used to describe many different distantly-related animals that typically have a long cylindrical tube-like body and no legs. Most animals called "worms" are invertebrates, but the term is also used for the amphibian caecilians and the slow worm Anguis, a legless burrowing lizard. Invertebrate animals commonly called "worms" include annelids (earthworms), nematodes (roundworms), platyhelminthes (flatworms), marine polychaete worms (bristle worms), marine nemertean worms ("bootlace worms"), marine Chaetognatha (arrow worms), priapulid worms and insect larvae such as caterpillars, grubs, and maggots.
In real life, worms vary in size from microscopic to over 1 metre (3.3 ft) in length for marine polychaete worms (bristle worms), 6.7 metres (22 ft) for the African giant earthworm, Microchaetus, and 55 metres (180 ft) for the marine nemertean worm (bootlace worm), Lineus longissimus. However, a huge number of fictional worms massively exceed this size.
Various types of worm occupy a small variety of parasitic niches, living inside the bodies of other animals. Free-living worm species may live on land, in marine or freshwater environments, or burrow.