A zoo (short for zoological garden or zoological park and also called an animal park or menagerie) is a facility in which animals are housed within enclosures, displayed to the public, and in which they may also breed. The term "zoological garden" refers to zoology, the study of animals, a term deriving from the Greek zÅon (Î¶á¿·Î¿Î½, 'animal') and lÃ³gos (Î»Ã³Î³Î¿Ï‚, 'study'). The abbreviation "zoo" was first used of the London Zoological Gardens, which was opened for scientific study in 1828 and to the public in 1857. The number of major animal collections open to the public around the world now exceeds to 1,000, around 80 percent of them are in cities. In the United States of America alone, zoos are visited by over 180 million people annually.