Allele frequency or Gene frequency is the proportion of all copies of a gene that is made up of a particular gene variant (allele). In other words, it is the number of copies of a particular allele divided by the number of copies of all alleles at the genetic place (locus) in a population.
It can be expressed for example as a percentage. In population genetics, allele frequencies are used to measure the amount of genetic diversity at the individual, population, and species level.