What animal classification is a worm?
"Worm" is a very broad term, that is most coloquially used to describe the earthworm.
The earthworm, along with other invertebrates such as leeches, are from the phylum Annelida , and are refered to as annelids .
Roundworms, on the other hand, belong to the phylum Nematoda , and flatworms belong to the Platyhelminthes phylum.
Below are examples of earthworms, roundworms, and flatworms, respectively.
(These images might be disturbing to some viewers)