the facility where wild animals are housed for exhibition
"We spent the whole afternoon walking around the zoo to see all the exotic animals up close."
A park where live animals are exhibited.
"We spent all afternoon walking through the zoo to see the elephants and giraffes up close."
In plain English: A zoo is a place where people keep wild animals in cages to watch and learn about them.
"We spent the whole afternoon at the zoo watching the elephants."
Usage: Use this term to refer specifically to an enclosed facility designed for public viewing of captive wild animals, rather than the general concept of many different kinds of creatures living together in nature or a chaotic situation. It is often confused with "menagerie," which historically implied a more private collection but now functions as a near-synonym depending on regional usage.
The word zoo began as a shortened form of "zoological garden" and eventually became the standard term for such places. A separate meaning referring to an animal lover also emerged later as a clipping from the words zoophile or zoophilia.