Primer3 is a widely used program for designing PCR primers (PCR =
"Polymerase Chain Reaction"). PCR is an essential and ubiquitous
tool in genetics and molecular biology. Primer3 can also design
hybridization probes and sequencing primers.
PCR is used for many different goals. Consequently, primer3 has
many different input parameters that you control and that tell
primer3 exactly what characteristics make good primers for your goals.