Clearer terminology could alleviate confusionIn the exploding field of stem cell biology, confusion pervades among some newcomers, and even veterans. The question is simple: When do we call a cell - stem cell?Some would argue that a fertilized egg is the ultimate stem cell. It is totipotent, giving rise to the embryo and extra-embryonic structures. The more fate-restricted cells of the inner cell mass of a blastocyst give rise to all body tissues and, with appropriate culture, to embryonic stem cells, which are considered to be pluripotent. Yet another term is reserved for the even more fate-restricted often multipotent stem...