Concept:Net migration measures the difference between people entering and leaving a country.
Explanation:Immigrants are people who come into a country to live.
Emigrants are people who leave a country to live elsewhere.
The difference between the number of immigrants and emigrants is called net migration.
It shows whether a country's population is gaining or losing people through migration.
Natural growth rate and natural increase are based only on births and deaths, not migration.
Census is an official count of the entire population.
Therefore, the correct definition matches net migration.
Answer:C. net migration