Biological immortality is the absence of a sustained increase in rate of mortality as a function of chronological age. A cell or organism that does not experience, or at some future point will cease, aging, is biologically immortal. However this definition of immortality was challenged in the new "Handbook of the Biology of Aging", because the increase in rate of mortality as a function of chronological age may be negligible at extremely old ages (late-life mortality plateau). But even though the rate of mortality ceases to increase in old age, those rates are very high (e.g., 50% chance of surviving another year at 110 or 115 years of age).No actual organism or individual cell is inviolably immortal (i.e. "invincible" or "indestructible"). Any real living object enjoying biological immortality can die upon receiving a sufficient injury or otherwise being killed or destroyed.