dNTPs (deoxynucleotide triphosphates) are the building blocks used in DNA synthesis. They consist of four types: dATP, dTTP, dCTP, and dGTP, corresponding to the bases adenine, thymine, cytosine, and guanine. During processes like PCR, dNTPs are incorporated into the growing DNA strand by DNA polymerase to replicate or amplify the target DNA sequence.