Glossary of population terms

Ageing population – An increasing average age in the population of a region due to declining fertility rates and/or rising life expectancy.

Birth rate – The number of births per 1,000 of population in a given year. This is different to fertility rate – see below. Birth rates may be high because a large number of women in a population are of child-bearing age, even if fertility rates (the number of children born per family) are low. See also “Demographic momentum”.

Carrying capacity – The maximum sustainable size of a population residing in a given ecosystem.

Census – An official record of the population in a country, including details such as population numbers, age, sex, and occupation.

Contraception (or birth control) – The use of artificial methods or other techniques to prevent pregnancy as a consequence of sexual intercourse. Methods of contraception or birth control include: condoms, diaphragms, contraceptive pills, intrauterine devices, contraceptive implants, spermicides, as well as male or female sterilisation.

Demographic dividend – Refers to the accelerated economic growth that may result from a decline in a country’s birth and death rates and the subsequent change in the age structure of the population.

Demographic transition – The historical shift of birth and death rates from high to low levels in a population. The decline of mortality usually precedes the decline in fertility, thereby resulting in rapid population growth during the transition period (see chart below for example). Demographic transition does not hold true in all circumstances, however.

Demography – The statistical study of human populations, including factors such as births, deaths, size and distribution. This is used to help illustrate the changing structure of human populations.

Dependency ratio – Relates the number of children (0-14) and older persons (65 years or over) to the ‘working-age’ population (15-64 years old). It is used to measure the pressure a productive population may face.

Earth Overshoot Day – The date on which humanity’s ecological resource consumption for the year exceeds Earth’s capacity to regenerate in that year.

Emigration – The process of leaving one country to take up permanent or semi-permanent residence in another.

Extreme poverty – A condition characterised by severe deprivation of basic human needs, including food, safe drinking water, sanitation facilities, health, shelter, education and information. As of 2015, a person is considered to be in extreme poverty if they live on less than $1.90 per day.

Family planning – The conscious effort of couples to regulate the number and spacing of births through artificial and natural methods of contraception.

Fertility – The actual reproductive performance of an individual, a couple, a group, or a population.

Global Gag Rule (also known as the Mexico City Policy) – A United States government policy that blocks U.S. federal funding for non-governmental organisations that provide abortion counselling or referrals, advocate to decriminalise abortion, or expand abortion services. 

Gross National Income (GNI) – A measurement of a country’s income. It includes all income earned by a country’s residents and businesses, including income earned abroad (e.g. property income).

Immigration – The process of entering one country from another to take up permanent or semi-permanent residence.

Infant mortality rate – The number of deaths under one year of age occurring among 1,000 live births in a given year.

Least Developed Countries – A list of countries that, according to the United Nations, exhibit the lowest indicators of socioeconomic development.

Life expectancy – The average number of additional years a person could expect to live if current mortality trends were to continue for the rest of that person’s life.

Mortality – Deaths as a component of population change.

Net migration – The net effect of immigration and emigration on a population in a given area and time period, expressed as an increase or decrease.

Net Migration Rate – The difference between the number of immigrants and the number of emigrants throughout the year. A positive net migration rate indicates that there are more people entering than leaving an area.

Population density – Population per unit of land area (e.g. number of people per square mile or people per square kilometre).

“Population explosion” (or “Population bomb”) – A rapid and dramatic increase in the size of a population. Can be caused by factors such as a sudden decline in infant mortality or an increase in life expectancy.

Population Growth Rate – The number of people added to (or subtracted from) a population in a year due to natural increase and net migration, expressed as a percentage of the population at the beginning of the time period.

Population momentum – The tendency for changes in population growth rates to lag behind changes in birth rates or fertility levels. If a country has a high birth rate, the large number of babies born at that time will start having children themselves a generation later.  That will increase the birth rate (see above) and population at that time, even if the fertility rate (roughly speaking, the size of each family) has gone down since they were born.

Population projection – Estimates of the total size and age structure of future populations. These projections may be used for resource allocation and planning.

Population pyramid – A bar chart, arranged vertically, that shows the distribution of a population by age and sex. By convention, the younger ages are at the bottom, with males on the left and females on the right (see chart below for example).

Pull factor – A positive aspect or condition that attracts people to move to that particular area (e.g. higher employment, better services, political stability, lower risk from natural hazards).

Push factor – A negative aspect or condition that motivates people to leave an area (e.g. lack of opportunities, concerns for safety, drought, flooding, poverty, war).

Rate of natural Increase or decrease – The difference between the number of live births and the number of deaths in a population over a given time period, expressed as a percentage.

Refugee – A person who has been forced to leave their country in order to escape war, persecution, or violence.

Replacement-level fertility – The total fertility rate (see below) at which a population exactly replaces itself from one generation to the next. The rate is roughly 2.1 children per woman, although it may vary with mortality rates.

Reproductive health – Implies that people are able to have a satisfying and safe sex life, including the freedom to decide if, when and how often to reproduce. A condition of reproductive health is to have adequate information as well as access to safe, effective, affordable and acceptable methods of family planning.

Sustainable Development Goals (SDGs) – A universal set of goals, targets and indicators that UN member states use to frame their agendas and political policies. The Sustainable Development Goals include a broad range of sustainable development issues, ranging from ending poverty and hunger, improving health and education, as well as combating climate change.

Total Fertility Rate – The average number of children born to each woman over her lifetime if she were to live to the end of her child-bearing years. This is an approximate guide to family size and the measure used by demographers and family planners to

Women’s empowerment – The process of increasing the capacity of women to make choices and to transform those choices into desired actions and outcomes.


Sign up to our newsletter to keep up to date with our work.

sign up