In the Hardy-Weinberg equilibrium equation (#p^2 + 2pq + q^2 = 1#), the term #2pq# represents the genotype frequency of heterozygotes (Aa) in a population in equilibrium. The term #p^2# represents the frequency of dominant homozygotes (AA) and the term #q^2# represents the frequency of recessive homozygotes (aa). #p# represents the allele frequency of allele A, and #q# represents the allele frequency of the allele a.
The sum of all of these terms is always equal to #1# (ie. #p^2 + 2pq + q^2 = 1# ) because those three frequencies represent all possible combinations of alleles. This description works best for a simple case study where there is a single gene locus and only two alleles for that gene locus.
