A pair of cells with closely similar optical properties are called matched cells. One cell is the sample cell while the other, the reference (or blank) cell contains the solvent or a reference solution. In double beam spectrometers, radiation is passed either simultaneously or alternately through the cells. In single beam instruments the cells are moved sequentially into the radiation beam.
Source:
PAC, 1988, 60, 1449. 'Nomenclature, symbols, units and their usage in spectrochemical analysis - VII. Molecular absorption spectroscopy, ultraviolet and visible (UV/VIS) (Recommendations 1988)' on page 1453 (https://doi.org/10.1351/pac198860091449)