How is evolution defined in genetic terms

In genetic term, evolution can be defined as any change in the frequency of allele in a population over a period of time.

Natural selection usually brings about changes in the genetic variation of a population of organisms over a period of time, this process might lead to speciation, which is formation of a new specie that is distinctly different from those that had been existing before. Genetic evolution through natural selection usually enhance an organism's ability to survive' in its environment.