stem cell

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An unspecialized cell that can give rise to one or more different types of specialized cells, such as blood cells and nerve cells. Stem cells are present in embryos and in various tissues of adult organisms and are widely used in scientific research.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun medicine, cytology A primal undifferentiated cell from which a variety of other cells can develop through the process of cellular differentiation.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an undifferentiated cell whose daughter cells may differentiate into other cell types (such as blood cells)