If you mean the difference between gene flow and gene migration than the answer is “none”, as they are synonyms.

The tell changes if you mean animal migration/gene flow.

Migrations are periodical movement (usually seasonal, but not necessarily) along precise and often repeated trails; the trigger for the migration may be local climate, local availability of food, the season of the year or for mating reasons. To be counted as a true migration, and not just a local dispersal, the movement of the animals should be an annual or seasonal occurrence or a major habitat change as part of their life.

Gene flow is the transfer of alleles or genes from one population to another.

A migration does not implicates a gene flow which usually occur trough a local dispersal (immigration of an animal from an A population to a B population).

If you mean the difference between gene flow and gene migration than the answer is “none”, as they are synonyms.

The tell changes if you mean animal migration/gene flow.

Migrations are periodical movement (usually seasonal, but not necessarily) along precise and often repeated trails; the trigger for the migration may be local climate, local availability of food, the season of the year or for mating reasons. To be counted as a true migration, and not just a local dispersal, the movement of the animals should be an annual or seasonal occurrence or a major habitat change as part of their life.

Gene flow is the transfer of alleles or genes from one population to another.

A migration does not implicates a gene flow which usually occur trough a local dispersal (immigration of an animal from an A population to a B population).