Fluorescence-activated cell sorting (FACS) is a specialized type of flow cytometry. It provides a method for sorting a heterogeneous mixture of biological cells into two or more containers, one cell at a time, based upon the specific light scattering and fluorescent characteristics of each cell. It is a useful scientific instrument, as it provides fast, objective and quantitative recording of fluorescent signals from individual cells as well as physical separation of cells of particular interest. Is most commonly used for isolating and analyzing specific cell populations from a heterogeneous mixture. It's widely applied in research areas like immunology, cancer biology, and stem cell research, where it's essential to study or culture specific cell types with distinct surface markers. FACS analyzes cells based on their fluorescent and light-scattering properties and can also physically sort cells into different containers based on these properties.