The difference between the size of the population to the end and the beginning of a period.The population change refers to change in the number of people during the specific time. The world population has not been stable. It has increased manifold. This subject is very closely related to demographics, the statistics of how many people there are in a given population.
This is actually due to changes in the number of births and deaths. For an extremely long period of human history until the 1800s, the world's population grew steadily but slowly. Large numbers of babies were born but they died early too. This was as there were no proper health facilities. Sufficient food was not available for all the people. Farmers were not able to produce enough to meet the food requirements of all the people. As a result, the total increase in population was very low.