Flow cytometry (cytometry = cell measurement) is a measurement method used in biology and medicine. A flow cytometer is the device used to perform flow cytometry. It allows the analysis of cells flowing individually at high speed past an electrical voltage or light beam. Depending on the shape, structure and/or staining of the cells, different effects are produced from which the properties of the cell can be deduced. In one form of flow cytometry, fluorescently labeled cells are sorted into different reagent vessels depending on their staining. Corresponding devices are called flow sorters or FACS (=fluorescence-activated cell sorting). Sometimes the term FACS (=fluorescence-activated cell scanning) is used with this meaning for devices that do not sort the cells, but only perform an analysis of their properties.