Cell lines are cells that have been isolated from a tissue or organ and cultured in a laboratory setting. These cells can divide and proliferate indefinitely, making them a valuable tool for studying cellular biology, disease mechanisms, drug testing, and other biomedical research applications. Cell lines are commonly used in research because they provide a consistent and reproducible model of a specific cell type, allowing scientists to study their behavior and response to various stimuli in a controlled environment. Many different cell lines are available, each representing a different cell type or tissue, making them a versatile resource for a wide range of research disciplines.