Population growth is a term that describes the rate and amount by which the number of people on planet Earth grows. The population growth of a region is affected by its birth rate, death rate, as well as the amount of migration to and from it. 

The birth rate describes the number of children born per thousand inhabitants each year.

Likewise, the death rate describes the number of deaths per thousand inhabitants each year.

Migration describes the way in which people move between different regions. The effects of migration are only visible in these regions, but are not reflected in the total population of the planet. There are two types of migration: migration that is directed in a certain region (immigration) and migration that is directed away from a certain region (emigration).

Let's study the population growth of an area by using an example. If 100 000 children are born in a certain area during a year, 85 000 people die during the same year, 5 000 people move to the region and 3 000 people move away from the region, what happens to the population? The answer is found by completing a simple equation: 100 000 - 85 000 + 5 000 - 3 000. The result is that the area's population grows by 17 000 inhabitants.