In vitro models are experimental systems used in scientific research that are conducted outside of a living organism, typically in a laboratory setting. These models are used to study biological processes, test hypotheses, and evaluate the effects of various substances or treatments on specific cells or tissues. In vitro models often involve culturing cells or tissues in a controlled environment that mimics the conditions found in the body, allowing researchers to observe and manipulate these systems in a controlled manner. These models can be used to study a wide range of biological processes, including cell growth and differentiation, drug testing, disease progression, and gene expression. In vitro models are valuable tools in research because they provide a simplified and controlled environment for studying complex biological systems.