The term for the change that occurs in an individual organism during its lifetime is called ontogeny. This process encompasses all developmental stages, from conception to maturity, reflecting the organism's growth, differentiation, and aging. Ontogeny includes various biological processes such as cell division, tissue development, and morphological changes. Understanding ontogeny is key in fields such as developmental biology and evolutionary biology, as it can provide insights into how organisms adapt to their environments and evolve over time.