Glossary of population terms

Abortion – The intentional termination of a pregnancy, through either safe or unsafe means. Abortion can be either surgical or medical (via medication). 

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 live births per 1,000 people in a population in a given time frame, usually one year. This is different from the fertility rate, which measures the average number of children born to each woman over her lifetime. Birth rates may be high because there is a large number of women of child-bearing age, even if fertility rates are low – see “population momentum”.

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

Comprehensive sexuality education – Teaches and empowers students not only to avoid pregnancy and sexually transmitted infections, but also to understand their bodies and to experience their sexuality and relationships in a healthy, respectful, and consensual way. 

Contraception (or birth control) – Methods of preventing pregnancy. Contraception includes traditional methods, such as withdrawal and periodic abstinence, and modern methods, such as condoms, diaphragms, contraceptive pills, intrauterine devices, contraceptive implants, spermicides, as well as male or female sterilisation.

Contraceptive prevalence – The percentage of women of reproductive age (typically defined as 15-49 years) who are currently using one or more methods of contraception. Unless otherwise specified, it typically refers only to women who are married or in a union (i.e. cohabitating with a partner), and includes both modern and traditional contraception methods. 

Demographic dividend – Refers to the accelerated economic growth that may result from a rapid decline in a country’s fertility rate, which leads to a lower dependency ratio (see below).

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. The 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 – The proportion of people in a population deemed too young or old to work (and thus considered economically dependent on others), compared to those of working age. It is calculated by adding the number of people under age 15 to the number of people over age 64, dividing that sum by the number of people aged 15-64, and multiplying that figure by 100. This definition misses the fact that in much of the world, people do not start working at age 15 and do not stop working (or contributing economically in other ways) at age 65.

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 – Information and methods, such as contraception and fertility treatments, that help people control whether and how many children they have. 

Fertility – The actual reproductive performance of an individual, a couple, a group, or a population. (See also Total Fertility Rate.)

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 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.

Natural increase or decrease– the amount of change in a population due to the balance of births and deaths. More births than deaths leads to an increase; more deaths than births to decrease. This excludes any changes as a result of net migration, so a country may see its population change in a different direction to the “natural” 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.

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

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. Growth rate expresses a proportion but the actual population used to calculate it changes from year to year. That means a decrease in the growth “rate” does not necessarily mean a decrease in the numbers of people by which the population increases. Globally, annual population growth rates have been going down for more than fifty years, but the number of people added each year has remained more or less constant in recent decades. That’s because each year the rate is calculated on the basis of a higher total population number than the year before.

Population momentum – The tendency for changes in population size to lag behind changes in fertility rates. If a country has a high fertility rate, the large number of babies born at that time will start having children themselves a generation later. Even if the fertility rate of that second generation decreases, the population is likely to continue growing simply because there is a large cohort of people of child-bearing age. 

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, showing the age distribution of a population. By convention, the younger ages are at the bottom, with males on the left and females on the right. 

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 (TFR) – The average number of children born to each woman over her lifetime if she were to follow prevailing patterns, or in simpler terms, the average number of children born to each woman.

Unintended pregnancy – A pregnancy that occurs to someone who had not planned to have a child at that time. It is a synonym of unplanned pregnancy, but distinct from unwanted pregnancy, because unintended pregnancies can also be wanted.

Unmet need for contraception – The condition of currently wanting to avoid pregnancy, but not using any modern method of contraception. 

Wanted fertility – An estimation of what the total fertility rate would be in a given population if all births were wanted.

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

*While we use “women” for the sake of simplicity, we are also referring to anyone who can become pregnant, including girls, transgender men, and non-binary people.