A thermal cycler is a laboratory device used in the process of polymerase chain reaction (PCR), which amplifies specific segments of DNA. It works by cycling through different temperature settings to facilitate the denaturation, annealing, and extension phases of PCR. This allows scientists to create millions of copies of a targeted DNA sequence for further analysis. Thermal cyclers are essential tools in molecular biology and genetics, enabling applications such as genetic testing, forensic analysis, and medical diagnostics. They come in various models, some with advanced features like real-time monitoring and programmable temperature profiles, enhancing their versatility in research and clinical settings.