Senescence

Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism. There are a number of hypotheses as to why senescence occurs; for example, some posit it is programmed by gene expression changes, others that it is the cumulative damage caused by biological processes. Senescence is not the inevitable fate of all organisms. A variety of organisms, including some cold-blooded animals, have negligible senescence. Whether senescence as a biological process can be slowed down, halted or even reversed, is a subject of current scientific speculation and research.

^{senecent cells  are cells that have stopped  division of cell, hence the ageing}