What is "american ostrich"

Rhea \Rhe"a\, n. [L., a proper name.] (Zo["o]l.) Any one of three species of large South American ostrichlike birds of the genera Rhea and Pterocnemia. Called also the American ostrich.

Note: The common rhea, or nandou ( Rhea Americana), ranges from Brazil to Patagonia. Darwin's rhea ( Pterocnemia Darwinii), of Patagonia, is smaller, and has the legs feathered below the knee.