1. Nested and Semi-Nested PCRs
A normal PCR usually involves only 1 round with an initial denaturing and, often, a final 10min extension step on top of the standard 30-45 cycles of a specific program that includes denaturation, annealing and extension steps. When people talk about nested or semi-nested PCRs, they are referring to a 2-round experiment that involves a second PCR using as DNA the previous amplified PCR products.