PCR, or polymerase chain reaction, is a laboratory technique used to amplify specific segments of DNA. It allows scientists to create millions of copies of a particular DNA sequence from a small initial sample. This process involves repeated cycles of heating and cooling, which separate the DNA strands and enable the binding of short DNA primers that target the desired sequence. The key components of PCR include DNA polymerase, which synthesizes new DNA strands, and nucleotides, the building blocks of DNA. PCR is widely used in various fields, including genetics, forensics, and medical diagnostics, making it an essential tool in molecular biology.