PCR is an abbreviation for "polymerase chain reaction." (POLL'-IM-ER-ACE). This term applies to a wide variety of different DNA tests that differ in reliability and effectiveness. Reliabilities of each kind of PCR test need independent verification. PCR itself doesn't accomplish DNA typing, it only increases the amount of DNA available for typing.
PCR uses constant regions of DNA sequence to prime the copying of variable regions of DNA sequence.
PCR typically uses two short pieces of known DNA called primers (small arrows below). These serve as starting points for the copying of a region of DNA.