Annealing is the second step in the polymerase chain reaction (PCR) process. During annealing, the temperature of the reaction is lowered to allow the primers to anneal or bind to the complementary sequences on the DNA template. The temperature of the annealing step depends on the melting temperature of the primer. The selection of the annealing temperature is critical, as too high of an annealing temperature prevents optimal binding of the primers to the templates, while too low of an annealing temperature can lead to non-specific binding and subsequently non-specific PCR products. Typically, the optimum annealing temperature is 3-5 degrees Celsius below the melting temperature.

In summary, annealing is a crucial step in the PCR process that allows the primers to bind to the complementary sequences on the DNA template. The temperature of the annealing step is critical and depends on the melting temperature of the primer.