Migration
Origionally used in reference to people deciding to change. Change resources, change behaviours, change a way of life, change their environment or their habitat. People on the move, going somewhere, progressing or escaping, changing.
It describes people moving from un-occupied land into non-occupied lands.
Emigration
Emigration is people deciding to move from occupied land into alternative occupied lands.
Immigration
Immigration is people being forced to moved from occupied land into occupied lands.
Migrant
To be a Migrant you have to settle on non-occupied land or be moving through occupied lands.
Immigrant
Any person who stops in an occupied land is an Immigrant.