AGE STRUCTURE Proportion of the population, or the number of people of each sex, at each age level in a population.

BIOPHYSICAL CARRYING CAPACITY The maximum population size that could be sustained under given technological capabilities.

BIOSPHERE The part of Earth, including the air and water, that can support life.

BIRTH RATE The number of births per l,000 population in a given year.

CARRYING CAPACITY The greatest number of living species (including humans) that can be supported in an area given its environmental conditions. For example, to raise one cow requires one acre of rich pastureland or ten acres of scrubland. See also BIOPHYSICAL CARRYING CAPACITY and SOCIAL CARRYING CAPACITY.

DEATH RATE The number of deaths per 1,000 population in a given year.

DEFORESTATION The loss of forests due to overcutting of trees. One consequence of deforestation is soil erosion, which results in the loss of protective soil cover and the water-holding capacity of the soil.

DEMOGRAPHIC MOMENTUM The tendency of a previously growing population to keep expanding even after reproductive rates have been reduced due to a large proportion of the population entering their reproductive years.

DESERTIFICATION The process by which semi-arid grassland becomes desert. This is usually caused by overgrazing, drought, and changing climate.

DEVELOPED COUNTRY A country with a high level of per capita income, industrialization, and modernization. Such countries usually have lower levels of population growth. The "more developed" regions of the world, according to the United Nations, include Europe, Canada, the United States, Australia, Japan, New Zealand, and the Soviet Union.

DEVELOPMENT Meeting the basic needs (economic, health, nutrition, social services, infrastructure) of people, and improving the standard of living in a society.

ECOSYSTEM The community of plants and animals interacting with one another and the environment.

EMIGRATION The process of leaving one country or area to take up residence in another.

ENDEMIC To be native of a particular people or country.

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

FINITE RESOURCES Resources that are limited in quantity. When they are used, they cannot be replaced.

HABITAT The place where a plant or animal species naturally lives and grows.

IMMIGRATION The process of entering one country from another to live permanently.

INFANT MORTALITY RATE The number of deaths of infants under one year of age in a given year, per 1,000 live births in that year.

INFRASTRUCTURE The foundation on which economic development is based. Includes the transportation, communication, electrical, and water supply systems of a nation or community.

LAND DEGRADATION To lower the quality of the land, making it less suitable for growing crops or raising livestock. Land degradation is caused by overcropping, overgrazing, and using farming methods that make the land less fertile.

LESS DEVELOPED COUNTRY A country with a low level of per capita income, industrialization, and modernization. Such countries usually have higher levels of population growth. Most are located in the tropical (low) latitudes in Africa, Asia, and Latin America.

LIFE EXPECTANCY The average number of years a person can expect to live.

NATURAL INCREASE The surplus (or deficit) of births over deaths in a population in a given time period.

NEWLY INDUSTRIALIZED COUNTRY A rapidly developing country. These include Saudi Arabia, Kuwait, the United Arab Emirates and Bahrain in the Middle East, and Taiwan, South Korea, Hong Kong and Singapore in Southeast Asia.

OZONE LAYER Chemical layer that protects living things on Earth by filtering harmful radiation from the sun.

POPULATION EXPLOSION A phrase used to describe rapid population growth in this century. This is caused by the world birth rate being much higher than the world death rate.

POPULATION GROWTH RATE The rate at which a population is increasing (or decreasing) in a given time period, expressed as a percentage of the base population.

POPULATION MOMENTUM The tendency for population growth to continue beyond the rate that is needed to exactly replace the dying population because of a relatively high concentration of people in the childbearing years.

RATE OF NATURAL INCREASE Birth rate minus the death rate, implying the annual rate of population growth without regard for migration. Expressed as a percentage.

REFUGEE A person who flees to a foreign country to avoid persecution in his/her own country or area. An environmental refugee leaves his/her country because he/she cannot survive given conditions on the land.

SOCIAL CARRYING CAPACITY The maximum population that could be sustained under a given social system and its associated patterns of resource consumption.

SUSTAINABLE DEVELOPMENT Practices in agriculture, economic development, health and education that lead to progress and meet the needs and desires of the current generation without decreasing the ability of future generations to meet their needs.

URBANIZATION Growth in the portion of a population living in areas of more than 2,500 people.

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