What is population?

Population denotes the total number of people living in a certain geographical area over a specific period of time.
Size of population means the units of population. Persons are the units that make total population. If there are more units or persons, the population size will be large and vice-versa. The size of population is never constant. It is ever changing.
Population growth refers to the additional number of people to the total population of a place or a country. Birth increases the population of a country.
Therefore, higher fertility is the symbol of high population growth rate. Unlike this, high mortality symbolizes low population growth rate of negative growth of population. Migration either increase of decreases the population of a country.