Avoid the misspelling/mispronunciation Girardia. A genus of parasitic flagellates that parasitize the small intestine of many mammals, including most domestic animals and humans; e.g., Giardia bovis in cattle, Giardia canis in dogs, and Giardia cati in cats. Many species have been described, but current research suggests that these should be reduced to only two or three. [Alfred Giard, Fr. biologist, 1846-1908]