A vivarium is a usually enclosed area for keeping and raising animals or plants for observation or research. Often, a portion of the ecosystem

Ecosystem

An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

 for a particular species is simulated on a smaller scale, with controls for environmental conditions.

A vivarium may be small enough to sit on a desk or table, such as a terrarium or an aquarium

Aquarium

An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...

, or may be a very large structure, possibly outdoors.