Ageing, or aging, is the combination of biological, psychological, and social processes that affect people as they grow older. Biologically, it involves physical maturation and changes in the body over time. Psychologically, it can involve shifts in cognitive function and emotional development. Sociologically, ageing entails changes in social roles, relationships, and societal expectations at different life stages. The experience of ageing is also shaped by cultural factors, with different societies having varying views on what it means to be a certain age. The human life course is often divided into stages like infancy, childhood, adolescence, adulthood, and old age, though these are somewhat arbitrary. Social gerontology is a field that specifically studies the social aspects of ageing.