Fluorescence-Activated Cell Sorting (FACS) is a laboratory technique used to separate and analyze cells based on their fluorescent properties. Cells are labeled with specific fluorescent dyes that bind to particular proteins or markers on their surfaces. When a mixture of cells passes through a laser beam, the fluorescent signals emitted are detected and analyzed. The FACS machine sorts the cells in real-time, directing them into different containers based on their fluorescence characteristics. This allows researchers to isolate specific cell types for further study, making FACS a valuable tool in fields like immunology, cancer research, and stem cell biology.