Concepts, classification, and the relationship between different types of senescence are discussed in this chapter. Senescence-related terminology frequently used in yeast, animal, and plant systems and senescence processes at cellular, organ, and organismal levels are clarified.
Keywords: Aging; Artificial senescence; Mitotic senescence; Monocarpic senescence; Natural senescence; Organ senescence; Organismal senescence; Polycarbic senescence; Postmitotic senescence; Senescence.