When migrated person never returns to his original place it is called permanent migration.
In most of the cases migration is seasonal, may be to work as labourer in farm during a particular season or migration of tribal people in search of fodder. This is short term migration.
In case of migration for jobs to city areas or to other countries, people work in migrated areas but visit their original places once or twice in a year. This is long term migration.
Thus, in most of the cases migration may be short term or long term and not permanent.
