Eels are an order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 of fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

, which consists of four suborders, 20 families

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

, 111 genera

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 and approximately 800 species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

. Most eels are predators. The term "eel" is also used for some other similarly shaped fish, such as electric eel

Electric eel

The electric eel , is an electric fish, and the only species of the genus Electrophorus. It is capable of generating powerful electric shocks, of up to six hundred volts, which it uses for both hunting and self-defense. It is an apex predator in its South American range...

s and spiny eel

Spiny eel

The name spiny eel is used to describe members of two different families of fish: the freshwater Mastacembelidae of Asia and Africa, and the marine Notacanthidae. Both are so-named because of their eel-like shape and sturdy fin spines....

s, but these are not members of the Anguilliformes order.
Eels are elongated fish, ranging in length from 5 centimetres (2 in) in the one-jawed eel (Monognathus

Monognathus

Monognathus, or Onejaws, is the only genus of the family Monognathidae of deep sea eel-like fishes. The name comes from the Greek monos meaning one and gnathos meaning jaw; a reference to the large mouth in comparison with the rest of the fish, and also the absence of an upper jaw...

 ahlstromi) to 4 metres (13.1 ft) in the slender giant moray

Slender giant moray

The slender giant moray or gangetic moray, Strophidon sathete, is the longest member of the family of moray eels. Specimen as large as 4 m have been recorded...

.