From Greek haima:blood and poiEtikos:creative, these are the stem cells capable of producing all lineages of white and red blood cells such as lymphocytes, granulocytes, platelets, erythrocytes, mast cells, macrophages and other cell types derived from monocytes.
The "Master" (blood forming) stem cells that are capable of recreating themselves and creating all of the other types of blood cells. They number 1 in 10,000 cells in bone marrow, and 1 in 1,000 cells in umbilical cord blood.