Polymerase chain reaction (PCR) is a technique used in molecular biology to exponentially amplify a specific segment of DNA. It allows researchers to quickly and efficiently replicate and analyze a specific target DNA sequence. PCR involves a series of temperature-controlled steps during which a DNA sample is heated to separate the two strands, cooled to allow primers to bind to the target sequence, and then heated again to activate a DNA polymerase enzyme that synthesizes new DNA strands. PCR is a versatile tool used in a wide range of applications, including genetic testing, disease diagnosis, forensic analysis, and gene cloning.