Net out-migration is when immigration is
emigration

Net out-migration is when immigration is less than emigration.

Explanation:

Net out-migration occur when a country or a city receives less people (immigration) than it sends to other places (emigration).

For example, if a country in a given year receives 100,000 people, but 200,000 nationals from that country emigrate to other places in the same year, then, the net out-migration is 100,000 people.

Most of the developing world has a net out-migration, while in the developing world is the opposite: net in-migration.