A thermal cycler is a laboratory device used in molecular biology to amplify DNA through a process called polymerase chain reaction (PCR). It works by repeatedly heating and cooling samples to facilitate the denaturation, annealing, and extension of DNA strands. This allows researchers to create millions of copies of a specific DNA segment for further analysis. Thermal cyclers are essential tools in various applications, including genetic research, medical diagnostics, and forensic science. They come with programmable temperature settings and can accommodate different sample sizes, making them versatile for various experiments involving DNA, RNA, and genetic material.