Stem cells
Stem cells are one of several varieties of cell that have the ability to renew themselves through division, and differentiate themselves into specialized cell types.
There is a gradient that corresponds to how well a particular stem cell can differentiate.
The two most common types, adult and embryonic, are multipotent and pluripotent respectively. Multipotent means that a stem cell can differentiate into similar types of cells, for instance blood cells only. Pluripotent means that they can turn into any of the 3 germ layer types.[1]
Even though embryonic stem cells can differentiate into more cell types than can adult stem cells, they require the destruction of an embryo which is akin to abortion.[2] That being said there is some research that shows that embryonic stem cells might be obtainable without destruction of the embryo, though this research is not definite yet.[3]
There are five categories of stem cells that correspond to their origin in the body: