What is the definition of stem cells and what's the debate all about?

Definition stem cell: All humans first start as a fertilized ovum, which is totipotent ("potential to become every cell"). After several days, it grows into an embryo, comprised of embryonic stem cells. Embryonic stem cells are still very unspecialized, and are described as being pluripotent ("potential to become a wide variety of cells"). Adult stem cells are multipotent ("a limited potential for differentiation"}.