The term that describes the movement of alleles into or out of a population is gene flow.

Here's a breakdown:

* Gene flow is the transfer of genetic material from one population to another. This can happen through migration, where individuals move from one population to another, or through the movement of gametes (sperm and egg cells).

* Alleles are alternative forms of a gene.

* Population refers to a group of individuals of the same species living in the same area and capable of interbreeding.

Gene flow can have a significant impact on the genetic makeup of a population. It can introduce new alleles, increase genetic diversity, and reduce genetic differences between populations.