Old age consists of ages nearing or surpassing the life expectancy of human beings, and thus the end of the human life cycle. Euphemisms and terms for old people include, old people (worldwide usage), seniors (American usage), senior citizens (British and American usage), older adults (in the social sciences), the elderly, and elders (in many cultures including the cultures of aboriginal people).Old people often have limited regenerative abilities and are more susceptible to disease, syndromes, and sickness than younger adults. The organic process of ageing is called senescence, the medical study of the aging process is gerontology, and the study of diseases that afflict the elderly is geriatrics. The elderly also face other social issues such as retirement, loneliness, and ageism.The chronological age denoted as "old age" varies culturally and historically. Thus, old age is "a social construct" rather than a definite "biological stage".