Zoos are one of the most visited tourist attractions worldwide - we should perceive them, therefore, not only as places where animals are kept, but also as places frequented by large numbers of people. This is why we talk of zoo tourism. However, there are different definitions of a zoo. This wide range of possible approaches to what actually the zoo is poses a major methodological problem for the research analysis as well as for the zoo management and related legislation. Zoos are historically and socially determined. We can talk not only about the evolution of zoos but also about the co-evolution of zoos alongside many types of zoos. Nowadays, there is no doubt that there is a large number of modern and naturalistic zoos oriented on conservation, but there are also many zoos designed as popular animal-based attractions where animals live in unsuitable conditions. The principal aim of this article is to introduce and discuss problematic approaches to what zoos are and to suggest a use of a wider zoo definition.