Stem cells may be defined as cells that exhibit two characteristics:
- Self-renewal - Stem cells can divide and divide and divide and still potentially remain undifferentiated.
- Potency - In this context, 'potency' refers to the potential of the stem cells to differentiate into specialised tissue.
Totipotent cells have the potential to become any cell at any stage in our development, including both adult cells and any extraembryonic (literally, 'outside the embryo') tissue, such as the placeta. A fertlised ovum (zygote) as well as all the cells up to the morula phase of development are totipotent.
Pluripotent cells have the potential to become any adult cell type but not any extraembryonic cells. Thus you wouldn't be able to 'grow' a human being with them alone.
Lastly, multipotent cells are somewhere in between pluripotent and mature cells in terms of specialising. They are capable of differentiating into mature cells of only a limited variety of types (e.g. just the various types of cells found in the heart).