Glossary of Gerontology Terms and Definitions

Ian C. Langtree - Writer/Editor for Disabled World (DW)
Published: 2009/01/11 - Updated: 2025/02/27
Publication Type: Glossaries, Definitions
Category Topic: Glossary and Definitions - Academic Publications

Page Content: Synopsis - Introduction - Main - Insights, Updates

Synopsis: This information provides a comprehensive glossary of terms and definitions related to gerontology, the multidisciplinary study of aging's biological, psychological, social, and health aspects. It includes detailed explanations of key concepts like Alzheimer's disease, life expectancy, biomarkers, and the compression of morbidity hypothesis, making it a valuable resource for understanding aging processes. The glossary is particularly useful for seniors, individuals with disabilities, caregivers, healthcare professionals, and researchers seeking to deepen their knowledge of aging-related topics and terminology. By offering clear definitions and context, it serves as an accessible guide for navigating the complexities of aging science and its implications for health and society - Disabled World (DW).

Introduction

Gerontology is the study of the social, cultural, psychological, cognitive, and biological aspects of aging. It includes:

• The study of physical, mental, and social changes in people as they age.
• The investigation of societal changes resulting from our aging population.
• The application of this knowledge to policies and programs.

The Gerontology field is distinguished from geriatrics, the branch of medicine that specializes in treating existing diseases in older adults.

Main Content

Gerontology Definitions and Terms

Aging

The life-long process of growing older; not just a later life experience

Alzheimer's Disease

The most common form of dementia. A degenerative disease that attacks the brain and results in impaired memory, thinking, and behavior.

Arthritis

A general term referring to disease of the joints. Arthritis includes over 100 diseases, often involving aches and pains in the joints and connective tissues. Most forms of arthritis are chronic, but proper treatment can frequently reduce symptoms substantially.

Apoptosis

Programmed Cell Death (PCD). This process removes unneeded cells and is particularly important for "sculpting" tissue and organ structure during embryo development (or larval metamorphosis in insects). Still, it may occur at any time, even in adult cells, when tissue needs to be remodeled.

Average Life Expectancy

The age at which 50 percent of the members of a population have died, when plotted on a standard survival curve. This statistic is normally calculated from birth but may be recomputed regarding expected years remaining at any age.

Bases

These are molecules with one or two nitrogen-containing ring structures. The biologically important bases are the purines Adenine and Guanine and the pyrimidines Cytidine, Thymine, and Uracil. DNA and RNA are composed of linked sequences of nucleotides.

Biomarker

A measurable parameter of physiological age that is a more useful predictor of remaining life expectancy than chronological age. The ability to measure biomarkers is essential in evaluating the efficacy of any potential life-extending intervention.

Blastocyst

A pre-implantation embryo that contains a fluid-filled cavity called a blastocoel.

Caloric Restriction (CR)

A diet in which calorie intake is reduced, compared with ad libitum (eat as much as you like) diets, without any reduction in nutritional requirements (protein, water, vitamins, or minerals).

Cancer

A clonal growth (cells all descended from one ancestral cell) that undergo continuing mitotic divisions and are not inhibited in their growth when they come in contact with neighboring cells (contact inhibition).

Cataract

A cloudiness or opacity that develops in the lens of the eye and results in poorer vision. Previously one of the leading causes of blindness in persons over 60, cataracts can now be surgically removed.

Centenarian

A person who is 100 years or older. There were 2,300 centenarians identified in the 1980 U.S. census.

Chromosome

The structures in the nucleus of the cell, consisting of DNA bound to histones and other proteins. The genes are made of DNA (although most of the DNA sequence is not part of any gene). Genes are arranged along the chromosomes in a continuous sequence. Chromosome protein structure allows for selective activation (genes are transcribed into protein) or silencing (genes are not expressed), and thus for differential expression of the genome in different cell types and expression of genes in appropriate sequences during the development of the organism or under various metabolic conditions.

Cleavage

The mitotic divisions of the early embryo that occur in the absence of growth to divide the embryo into too many smaller nucleated cells.

Cloning

The use of the chromosomes from an adult cell to create an identical twin (copy) of an organism by inserting the adult nucleus into an egg from which the nucleus has been removed, stimulating embryogenesis, and implanting the embryo into the uterus of a surrogate mother. Reproductive cloning of sheep, mice, goats, cows, pigs, and mules has been widely accomplished.

Cohort

A set of people born during a specific period; also a set of people born during a historical era that creates different inter-cohort characteristics such as size, composition, experiences, and values.

Dementia

A syndrome characterized by a decline in intellectual functioning. May be caused by more than 70 diseases, the most common being Alzheimer's Disease.

Demography

The study of a population and those variables bringing about change in that population. Variables studied by demographers are age, sex, race, education, income, geographic trends, birth, and death.

Diploid Cell

A cell with pairs of homologous chromosomes.

DNA

An abbreviation for Desoxy Ribonucleic Acid. Double-stranded DNA molecules consist of antiparallel (running in opposite directions) chains of nucleotides in which the sugar component is desoxyribose. The chains are arranged in a double helix with the two chains wrapped around each other and bound together so that each "A" is paired with a "T" (A: T pair) and each "G" is paired with a "C" (G: C pair). Thus, new identical antiparallel sequences can be copied along their lengths when the chains unwind and separate. Thus, DNA is self-replicating.

Compression of Morbidity Hypothesis

Prof. James F. Fries, M.D., a Stanford University School of Medicine rheumatologist, established the "compression of morbidity" hypothesis in 1980. He suggested that if the onset of disability due to age-related diseases and conditions could be postponed to a greater degree than average life expectancy would increase, then total lifetime disability could be compressed into a shorter average period. The cumulative average lifetime disability would also be reduced.

Disposable Soma

From an evolutionary point of view, the Prime Directive of any organism is to transform available energy from the environment into the maximum number of progeny. Part of the energy is consumed in the maintenance of the organism's somatic (body) tissues (for growth and repair of injury), and part is used to propagate the germ-line tissues.

Egg

A female haploid germ cell.

Entropy

A measure of the level of disorder or randomness in a closed system. It can be thought of either in the sense of thermodynamic/metabolic processes or the increasing molecular disorder in a structure. It can be thought of as the same process by which erosion occurs when soil is exposed to rain and wind.

Evidence-Based Medicine

The practice of medicine with treatment recommendations that have their origin in objective tests of efficacy published in the scientific literature rather than anecdotal observations.

Fecundity

The ability to produce offspring. High fecundity means the ability to produce progeny rapidly and in large numbers. In the demography of human populations, fecundity is the physiological ability to reproduce, as opposed to fertility.

Fertility

Reproductive Potential. In demography, the number of births per year divided by the number of women of childbearing age is expressed as a rate.

Gene

a functional unit of heredity. It is a segment of DNA located at a specific site on a chromosome whose length is typically several thousand base pairs long. A gene directs the formation of an enzyme or other protein using processes of transcription and translation. More precisely, a gene is a sequence of DNA that can be activated and copied into messenger RNA (or mRNA) by the process known as transcription.

Generation

Though popularly used as a synonym for cohort, the term is also applied within the context of the family. Children form one generation, their parents another, their grandparents a third, and so on.

Geriatrics

The branch of medicine specializing in the health care and treatment of older persons. It is defined by the World Health Organization as the branch of medicine that is concerned with the health of older adults in all aspects: preventative, clinical, remedial, rehabilitative, and continuous surveillance.

Genotype

The genetic makeup of a cell, organism or group of organisms, concerning a single trait or group of traits; the total of genes transmitted from parents to their offspring.

Genome

The complete collection of genes in the nucleus of each cell of our bodies. There are now known to be somewhat less than 25,000 genes in the human genome.

Geriatrics

A branch of Internal Medicine concerned with the care and treatment of older persons and the treatment and amelioration of diseases of old age and frailty.

Gerontology

The multidisciplinary study of all aspects of aging, including health, biological, sociological, economic, behavioral, and environmental.

Germ Cell

Either an egg or a sperm cell.

Gerontology

A branch of biology focusing on the common mechanisms of aging across all multicellular species. Gerontologists, for example, are keen to understand species that exhibit gradual or negligible senescence over a long time interval. In this context, gerontologists may study yeast, worms, fruit flies, mice, rockfish, tortoises, bats, parrots, humans, and other creatures exhibiting exceptional longevity.

Gerontome

The subset of the genome whose genes affect longevity, either significantly reducing or increasing the average lifespan of an organism.

Glaucoma

A disease in which pressure builds up within the eye and causes internal damage, gradually destroying vision. Often hereditary, glaucoma usually affects persons after 40. Symptoms may be blurred vision, difficulty in focusing, loss of peripheral vision, or slow adaptation to severe and irreversible loss of vision has occurred. While no method exists for preventing glaucoma, diagnosing the disease in its earliest stages can prevent further damage.

Gompertz Model

A class of statistical models first proposed by the nineteenth-century British actuary Benjamin Gompertz, in which the hazard rate for death rises exponentially with increasing age of the organism (at least after an initial period of high risk of mortality at birth and infancy and much lower risk in late childhood and adolescence). Today, the Wibel Model is superior to the Gompertz Model, as it more accurately explains observed demographic data.

Grandparent

A role that an older person assumes when their children have children of their own.

Grand-parenting Hypothesis

This is the supposition that is abruptly terminating reproduction at a particular age (menopause) and prolonged survival of human females after menopause may have been selected for because of better success in child-rearing (and hence the survival of the gene pool) when older women focus their resources on the welfare of their grandchildren and thereby increase their likelihood of survival of the tribe, rather than investing energy in producing more and more children of their own, and potentially compromising the reproductive success of their more mature offspring.

Haploid Cell

A cell with half the normal complement of chromosomes, typically a germ cell.

Hayflick Limit

The limit to the number of times a cell can divide during serial cell culture. The value of this limit as a predictor of the maximum lifespan of the organism is still unproven.

Homeostasis

The physiological capacity of an organism to regulate itself by rapidly restoring internal conditions following a sudden perturbation in the external environment.

Inner Cell Mass

Cells that give rise to the embryo proper and that arise from the inner cells of an early pre-implantation embryo.

Life History

The combination of age-specific survival probabilities and fertilities characteristic of a species; the timetable of individual development and aging for a representative organism (e.g., in humans, from fertilization conception, to embryogenesis, implantation/placentation; organogenesis/fetogenesis, birth, infancy, adolescence, puberty, adulthood, menopause, loss of vitality, frailty/morbidity, and ultimately, death mortality.

Lifespan

The maximum lifespan of a species is the characteristic observed age of death for its very oldest individual(s) (e.g., for humans 122+ years). On the other hand, the average lifespan is the age at which 50 percent of a species or group members have died. Over the last two centuries, average life expectancy has risen significantly, while maximum lifespan has hardly changed.

Life Cycle

(1) The entire course of a person's life, from infancy to old age. Health, social roles and expectations, and socioeconomic status change as an individual develops.

(2) The genetically prescribed course followed by all living organisms, including humans, from conception to death through stages of development and change.

Longevity

The condition or quality of being long-lived.

Longevity Genes

Gerontic genes that extend or shorten the maximum lifespan of a species.

Meals-on-Wheels

A program that delivers meals to the homebound.

Medicare

A federal entitlement program of medical insurance for persons age 65 and over provided through the Social Security system. Covers mostly acute health care needs.

Menopause

The time of life when a woman ceases to menstruate and can no longer become pregnant, usually about age 45 to 50.

Multi-potent Cell

A stem cell that has limited capabilities for specialization, normally within a specific tissue type.

Mutation

Any change in DNA structure which alters the established order of the bases. This may cause a gene (or series of genes) to fail to be activated normally (either to be silenced or, conversely, to be expressed inappropriately) or may cause a gene to express a protein with abnormal structure (and hence abnormal function).

Necrosis

Cell death secondary to traumatic injury. Necrosis invariably induces a subsequent inflammatory reaction, as distinguished from apoptosis, which does not.

Nucleotides

molecules that consist of a purine or pyrimidine base, a ribose or desoxyribose sugar, and a phosphate group.

Osteoporosis

A decrease in density of the bones causing structural weakness throughout the skeleton. Fractures can result from even a minor injury or fall. Some bone loss normally occurs in older adults. Still, osteoporosis develops most often in white women after menopause.

Parthenogenesis

The development of an individual from an egg without fertilization.

Phenotype

The external manifestations of gene expression, whether at the level of the cell (e.g., muscle cells are long and thin and contain contractile fibrils; nerve cells have excitable membranes and communicating processes) or the organism (e.g., the giraffe has a long neck; a leopard, spots, and elephants, trunks).

Pluripotent Cell

A cell capable of giving rise to most tissues of an organism.

Progeria

A human disease or syndrome in which some characteristics of senescence are accelerated so that relatively young individuals appear prematurely aged. Examples include Hutchinson-Guilford Syndrome (HGS), a rare autosomal-dominant disorder with a classic withered presentation leading to early death in the teenage years.

Protein

A linear sequence of Amino Acids whose three-dimensional shape determines a particular function in the body.

Proteome

The collection of all proteins in the body of an organism. For humans, it is estimated that there are 250,000 - 300,000 proteins, of which fewer than half have been cataloged thus far.

Retirement

Period or life stage following termination of and withdrawal from a regular job and income from employment. Difficult to delimit because some older persons retire from one job and take another full or part-time job.

Reproductive Cloning

The creation of an embryo using SCNT to create a new (identical twin) individual of that species.

Reprogenic

Techniques at the intersection of reproductive medicine and genetics for manipulating gametes and embryos.

RNA: Ribonucleic Acid

RNA is a sequential chain of the nucleotides Adenosine, Guanosine, Thymidine, and Uridine. In RNA, the sugar molecules are ribose. RNA is typically single-stranded. The sequence of most RNA molecules is copied from specific DNA sequences by enzymes in a process called transcription.

Senescence

That portion of aging that begins at older ages, after one passes the point of minimum mortality, around age 12 for humans. More specifically, senescence is not a single disease. It is characterized as a generic, increased susceptibility to various age-related chronic diseases and a reduced ability to repair the damage.

Social Security

A national insurance program that provides income to workers when they retire or are disabled and to dependent survivors when a worker dies. Retirement payments are based on workers' earnings during employment.

Somatic Cell

A diploid cell of the body; a cell other than a germ cell (an egg or a sperm).

Somatic Cell Nuclear Transfer (SCNT)

The transfer of a cell nucleus from a somatic cell into an enucleated egg (one from which the nucleus has been removed).

Sperm

A male haploid germ cell.

Stem Cell

An undifferentiated cell that possesses the ability to divide for indefinite periods in culture and may give rise to highly specialized cells of each tissue type. There are embryonic stem cells found in the blastocyst known to be totipotent. In contrast, adult stem cells found in bone marrow, for example, may only be pluripotent (not able to produce an entirely new organism but can produce all three tissue types).

Survival Function

The probability that an individual will remain alive at a particular age. The percentage of an experimental cohort that remains alive throughout the experiment.

Telomere/Telomerase

Repetitive DNA sequences at the four ends of the chromosome, which an RNA-containing enzyme can lengthen called telomerase.

Therapeutic Cloning

The creation of a several day-old embryo using SCNT to harvest the cells for subsequent tissue-culture amplification and injection into a host for therapeutic purposes (presumably without fear of GVH [Graft vs. Host] Disease or immunological rejection).

Totipotent Cell

A cell having an unlimited capacity to create a new organism. A totipotent cell can specialize into an embryo, extra-embryonic membranes and tissues, and all post-embryonic tissues and organs.

Translational Research

Clinical investigation with human subjects (patients or normal volunteers) in which knowledge obtained from basic research with genes, cells, or animals is translated into diagnostic or therapeutic interventions that can be applied to the treatment or prevention of disease or frailty.

Trophobastic Cells

Cells that contribute to the placenta but not to the embryo itself and which are required for an embryo to implant into the uterine wall.

Also see our How Long Will I Live - Life Span Expectancy Chart showing the average number of years you will live for according to which country you live in.

Insights, Analysis, and Developments

As populations worldwide continue to age rapidly, resources like this glossary play a critical role in fostering a deeper understanding of the challenges and opportunities associated with aging. Whether addressing the needs of older adults or advancing research into age-related diseases, having a clear grasp of gerontology's foundational terms is essential for informed decision-making and effective communication across disciplines

Author Credentials: Ian is the founder and Editor-in-Chief of Disabled World, a leading resource for news and information on disability issues. With a global perspective shaped by years of travel and lived experience, Ian is a committed proponent of the Social Model of Disability-a transformative framework developed by disabled activists in the 1970s that emphasizes dismantling societal barriers rather than focusing solely on individual impairments. His work reflects a deep commitment to disability rights, accessibility, and social inclusion. To learn more about Ian's background, expertise, and accomplishments, visit his full biography.