It refers to the act of entering a foreign country to live there permanently.
Here's a breakdown:
* Ein - This prefix means "in" or "into."
* Wandern - This means "to wander" or "to migrate."
* -ung - This is a suffix that turns a verb into a noun, indicating an action or process.
So, "Einwanderung" literally means "in-wandering," signifying the process of entering a new country to live.