In vitro models are experimental systems that are conducted outside of a living organism, such as in a test tube or petri dish. These models are commonly used in scientific research to study biological processes and test the effects of various substances on cells or tissues. In vitro models can be used to investigate basic cellular functions, disease mechanisms, drug development, and toxicology. These models provide a controlled environment that allows researchers to manipulate variables and observe specific outcomes, without the complexities and ethical considerations of working with live organisms. Additionally, in vitro models can offer a more cost-effective and time-efficient way to conduct experiments compared to in vivo studies.