Stem cells are unspecialized cells that have two defining properties: the ability to differentiate into other cells and the ability to self-regenerate.
According to The Harvard Stem Cell Institute, Stem cells are unique in their ability to self-renew: to divide and create two cells, each identical to the original. Understanding stem cell self-renewal is central to understanding how organisms are made and maintained, and may lead to insights that permit physicians to modulate tissue regeneration and repair in their patients.
[ via The Harvard Stem Cell Institute ]