In vivo models refer to research conducted on living organisms, such as animals, to study biological processes, diseases, and the effects of various treatments. These models are used to better understand how a particular substance or treatment will behave in a living system and to evaluate its safety and efficacy. In vivo research allows scientists to study complex interactions in a whole organism, rather than in isolated cells or tissues, providing a more complete picture of biological processes. These models are crucial for drug development, disease research, and understanding human health and physiology.