A zoo, or zoological garden, was a place where animals and plants were kept in captivity to observe or study their characteristics. Zoos were managed by zookeepers. (VOY: "Life Line")
In 2254, The Keeper offered to help Christopher Pike with the reclaiming of Talos IV's surface by furnishing a wide variety of plants from the zoological gardens. (TOS: "The Cage", "The Menagerie, Part II")
In 2266, Doctor McCoy described a microscopic view of a virus on Miri as "a veritable zoo of bacteria." (TOS: "Miri")
In 2269, the crew of the USS Ariel was captured by the Lactrans on a survey mission. They were placed in a Lactran zoo until they were freed, about six weeks later, by the crew of the USS Enterprise. (TAS: "The Eye of the Beholder")
Doctor Mora Pol was concerned that Odo would be placed in a prison or even a zoo if the reason for him repeatedly transforming into a dangerous creature, in mid-2370, was not discovered. (DS9: "The Alternate")
Brentalia, a planet that served as a sanctuary for endangered species, included a zoo. (TNG: "Imaginary Friend")
During a meeting between high-ranking members of the Federation Alliance in 2374, Romulan Senator Letant made a derogatory remark against Martok, telling an aide, "Klingons can be quite entertaining, don't you agree? Every Romulan zoo should have a pair!" (DS9: "Tears of the Prophets")
Amanda Rogers' parents used to jokingly refer to her three dogs as her zoo. (TNG: "True Q")