While the term is also used to name prejudice and discrimination against adolescents and children, including ignoring their ideas because they are too young, or assuming that they should behave in certain ways because of their age, the term is predominantly used in relation to the treatment of older people. Moreover, it has been pointed out that stigmatization does not only occur outside of the cohesively imagined group of the elderly but likewise takes place within the stigmatized group itself. Fear of death and fear of disability and dependence are major causes of ageism; avoiding, segregating, and rejecting older people are coping mechanisms that allow people to avoid thinking about their own mortality.
It can also be passive and covert (e.g., a movie that shows only young people inhabiting a locality and no children, infants or old people are shown in the area to drive the notion that the place is 'young and romantic').
Ageism in common parlance and age studies usually refers to negative discriminatory practices against old people, people in their middle years, teenagers and children. There are several forms of age-related bias. Adultism is a predisposition towards adults, which is seen as biased against children, youth, and all young people who are not addressed or viewed as adults. Jeunism is the discrimination against older people in favor of younger ones. This includes political candidacies, jobs, and cultural settings where the supposed greater vitality and/or physical beauty of youth is more appreciated than the supposed greater moral and/or intellectual rigor of adulthood. Adultcentricism is the "exaggerated egocentrism of adults." Adultocracy is the social convention which defines "maturity" and "immaturity," placing adults in a dominant position over young people, both theoretically and practically. Gerontocracy is a form of oligarchical rule in which an entity is ruled by leaders who are significantly older than most of the adult population. Chronocentrism is primarily the belief that a certain state of humanity is superior to all previous and/or future times.
Based on a conceptual analysis of ageism, a new definition of ageism was introduced by Iversen, Larsen, & Solem in 2009. This definition constitutes the foundation for higher reliability and validity in future research about ageism and its complexity offers a new way of systemizing theories on ageism: "Ageism is defined as negative or positive stereotypes, prejudice and/or discrimination against (or to the advantage of) elderly people on the basis of their chronological age or on the basis of a perception of them as being 'old' or 'elderly'. Ageism can be implicit or explicit and can be expressed on a micro-, meso- or macro-level" (Iversen, Larsen & Solem, 2009).
Other conditions of fear or aversion associated with age groups have their own names, particularly: paedophobia, the fear of infants and children; ephebiphobia, the fear of youth, sometimes also referred to as an irrational fear of adolescents or a prejudice against teenagers; and gerontophobia, the fear of elderly people.