Flow cytometry is a laboratory technique used to analyze the physical and chemical characteristics of cells or particles in a fluid as they pass through a laser. It measures various properties, such as size, complexity, and the presence of specific markers on the cell surface, by detecting the light scattered by the cells and the fluorescence emitted from labeled antibodies. This method is widely used in research and clinical settings, including immunology, oncology, and hematology, to identify and sort different cell types. It allows scientists to gather detailed information about cell populations quickly and accurately, making it a valuable tool in both diagnostics and research.