Indefinite lifespan represents the continuation of life without the limit of biological ageing. It is different from immortality, because indefinite lifespan does not imply an inability to die of other causes.
- Hamid, Farrukh. (2015). Panacea in My Veins: Stem Cell Facts and Fiction. ISBN 1482832593. "You may call it semantics, but the term 'indefinite lifespan', represents a more achievable state than immortality, since it implies freedom from death by aging or infirmity but does not make one unable to die."
- Shostak, Stanley. (2012). The Evolution of Death: Why We Are Living Longer. ISBN 079148081X. "Thus, as life cycles, lifecycles move from germ cells capable of reprogramming to stem cells capable of proliferating and initiating the programs of precursor and transit cells, interacting with other tissue and with the external environment, and differentiating in tissues in organs. Mortality represents an end of these processes; negligible senescence and indefinite life span represent their continuation."