Abstract <p>Various views on the “correct” definition of aging are analyzed. It is emphasized that a huge number of such definitions have emerged in recent decades, and several million scientific publications devoted to this topic can be found online. At the same time, most gerontologists based their definitions on the premise that aging (with various modifications) is a set of age-related changes in the body that lead to an increased probability of death. However, as numerous new data emerged in gerontological research, many specialists began to question the suitability of this “classical” definition. This was due, among other things, to the identified impact of long-term chronic diseases such as HIV or COVID-19 on age-related mortality dynamics, to the dramatic changes in recent decades in the understanding of cellular aging and the relationship between aging and various age-related diseases, as well as to the correct methodology for determining biological age. The apparent lack of progress in fundamental gerontology to date and the emergence of a large number of studies in which the presence/absence of aging in the studied organisms was in no way linked to the obtaining survival curves also played a significant role. The evolution of approaches to defining aging is discussed, as well as potential future modifications to this definition.</p>