Cellular heterogeneity refers to the differences in the characteristics and functions of cells within a single tissue or organism. These variations can arise from genetic differences, environmental influences, or the cells' developmental stages. Understanding cellular heterogeneity is crucial for studying complex biological systems, such as cancer or immune responses, where diverse cell types can affect overall function and behavior. This concept is important in fields like stem cell research and personalized medicine, as it helps scientists identify specific cell populations that may respond differently to treatments. By recognizing and studying these differences, researchers can develop more effective therapies tailored to individual patients' needs.