A microplate reader is a laboratory instrument used to measure the optical properties of samples in microplates, which are flat plates with multiple wells. These devices can detect various signals, such as fluorescence, absorbance, and luminescence, making them essential for experiments in fields like biochemistry and molecular biology. Microplate readers are commonly used in applications like enzyme-linked immunosorbent assays (ELISA), cell viability assays, and drug discovery. They allow researchers to analyze multiple samples simultaneously, increasing efficiency and throughput in scientific studies.