1 – What Entity Could Be Called a Stem Cell?

Frequently the properties of stem cells have been extrapolated on the basis of analysis of various phenotypically defined cell populations in which the functional stem cells do not represent a majority. This practice contributed to the confusion in the field that is already highly complex by its nature. In order to avoid this confusion as much as possible, in this chapter we discuss in detail the above-mentioned problem, striving to give a direction for the correct understanding and interpretation of the literature data presented in this book.