A type of long, slender fish (somewhat resembling a snake in appearance) that spends most of its life in freshwater but breeds in the ocean, and consequently is found in marshy areas where freshwater has access to the sea. Species of eel are found all over the world.
An eel farm is owned by Agatha Timms, who bet half its shares with Ludo Bagman that the final of the 1994 Quidditch World Cup would be a week long (GF7).
Eels are not commonly eaten in the U.S. but eel pie, for instance, is eaten in Britain. To take an example from one of JKR's favourite books, when in C.S. Lewis' The Silver Chair, the Marsh-wiggle Puddleglum offered Jill and Eustace eel stew but was dubious about whether humans could eat it or would enjoy it, he was merely giving one of his typical gloomy observations about life, the universe, and everything.