Short pre-existing polynucleotide chain attached to a complementary stretch in template deoxyribonucleic acid (DNA) to which new deoxyribonucleotides can be added by DNA polymerase.
Source: PAC, 2018, 90, 1121. 'Terminology of bioanalytical methods (IUPAC Recommendations 2018)' on page 1150 (https://doi.org/10.1515/pac-2016-1120)