cells with an unlimited capacity to divide and the ability to turn into most of the cells or tissues in the body; derived from inner cell mass cells from blastocyst stage embryos, primordial germ cells from fetal tissue, and possibly by somatic cell nuclear transfer; do not have the potential to form an individual organism because they do not have the capacity to give rise to the cells of the placenta or other extraembryonic tissues necessary for implantation, nor can they support fetal development in the uterus; useful application as a renewable source of replacement cells and tissue to treat a myriad of diseases, conditions and disabilities, i.e. stem cell therapy.