A biological cell that can differentiate into a particular cell type is called a progenitor cell. This capability is shared by progenitor cells and stem cells. Progenitor cells are more specific than stem cells, though. Only their "target" cell type can be differentiated by progenitor cells. Because stem cells can replicate indefinitely while progenitor cells can only divide a finite number of times, this is the key distinction between stem cells and progenitor cells. There is still discourse over the precise definition, and the idea is still designing.