Answer:
Birth Rate
Now, this might seem very obvious to you, but when babies are born, it results in a population change! Social scientists who study this trend have some key terms, though. First, the fertility rate in a country refers simply to the number of children born. This is different from the fecundity rate, which is the number of children who could be born in a given society. In other words, fecundity is the biological capacity of humans to produce children.
Death Rate
Just as when babies are born, when members of a society die it changes the population. This might be a bit morbid to think about, but scientists refer to this as the mortality rate, which is simply the number of deaths that occur in a society. This is usually calculated by looking at the number of deaths per 1,000 individuals. In the United States, for example, the death rate is 8/1000 people. Just like birth rate, the death rate in a country depends on things such as availability of quality medical care, disease, war, or famine.
Migration Rate
One important factor that accounts for a change in population is migration. At the broadest level, migration refers to movement; it's the flow or circulation of people in societies. There are two kinds of migration: emigration and immigration. Emigration means to leave one's own country for another. Immigration means to enter into a country other than one's own.