Definitions of stem cell on the Web:

• A cell from which other types of cells can develop.
  plan2005.cancer.gov/glossary.html

• Stem cells give rise to normal blood components including red cells, white cells and platelets. Stem cells are normally located in the bone marrow and in the blood and can be harvested for a transplant.
  www.myeloma.org.uk/pages/pi4.htm

• A "generic" or undifferentiated cell that can make exact copies of itself indefinitely, and can become specialized for various tissues in the body. a
  www.mise.org/mise/index.jsp

• An unspecialized cell that gives rise to a specific specialized cell, such as a blood cell.
  www.ukhealthcare.uky.edu/patient/glossary/glossary-s.htm

• A young, precursor cell that originates in the bone marrow and serves as the “parent cell” to all other blood cells in the body. Red blood cells, white blood cells and platelets all evolve from stem cells.
  www.cancercenter.com/stem-cell/stem-cell-glossary.cfm

• Cells that can give rise to other types of cells; they are produced both during embryonic development and in the adult body. Embryonic stem cells begin with the ability to become any cell type, and quickly differentiate into cells committed toward a certain type of tissue, eg, blood, skin, or neural stem cells. These are termed multipotential stem cells, because they further divide into cells with a particular function, such as red and white blood cells and platelets. ...
  www.myelin.org/glossary.htm

• An undifferentiated cell that possesses the ability to divide for indefinite periods in culture and may give rise to highly specialized cells of each tissue type. There are embryonic stem cells found in the blastocyst that are known to be totipotent, while adult stem cells found in bone marrow, for example, may only be pluripotent (not able to produce an entire new organism but are able to produce all three tissue types).
  images.antiagingconference.com/files/1103/aagateway/glossaryofterms.asp

• A"generalized" cell whose division results in other specialized cells. Its descendents have the potential to develop into several different types of mature cells.
  www.ctrf.org/glossary.cfm

• Reproduce indefinitely and have the capacity to develop (differentiate) into a large number of different cell types.
  www.hfea.gov.uk/Glossary

• An undifferentiated active somatic cell that undergoes division and gives rise to other stem cells or to cells that differentiate to form specialized cells.
  www.fao.org/docrep/003/X3910E/X3910E22.htm

• an undifferentiated type of body cell found in bone marrow, growing tissues, and embryonic tissue. The physical location of the stem cell, and the hormonal or growth influences that surround it, will determine what type of adult cell it will become.
  www.qimr.edu.au/qimr_glossary.html

• A primitive, unspecialized cell that has the capacity to develop highly specialized function when grown in the appropriate environment and treated with specific growth factors. Stem cells for the retina reside in the ciliary body, a specialized structure that sits on either side of the iris, near the retina. They usually lie dormant in the adult. Stem cells have now been isolated and are being evaluated as a potential source for RPE and photoreceptor cells for transplants.
  www.blindness.org/research/glossary.asp

• There are several kinds of stem cells, only one of which is controversial. Stem cells taken from very early human embryos are the hot button, but these cells also occur in many tissues of adults. In general, a stem cell is capable of developing into a number of different kinds of cells, depending on what chemical signals it receives. In bone marrow, for example, there are stem cells that can develop into several kinds of white blood cells or red blood cells, depending on the body’s needs.
  www.med.umich.edu/genetics/glossary/

• An undifferentiated cell from which specialized cells develop.
  www.biotech.ca/EN/glossary.html

• a cell that can self-renew and give rise to more differentiated cell types.
  www.oup.com/uk/booksites/content/0199264724/student/glossary.htm

• A type of primitive cell that can transform into and generate other cells.
  www.bmgnri.com/Glossary.htm

• Early (immature) blood cell
  www.cancerbacup.org.uk/Cancertype/Childrenscancers/General/Sometermsexplained

• A progenitor, or "primitive" cell ancestor, of almost all the blood cell types. These immature cells are found in the bone marrow and develop into red cells, white cells, or platelets. Learn more.
  www.cmlsupport.com/cmlglossary.htm

• These are primitive cells in marrow that are required to make red cells, white cells and platelets (see “hematopoiesis”). Generally, the stem cells are largely found in the marrow but some leave the marrow and circulate in the blood. Using special techniques, the stem cells in blood can be collected, preserved by freezing and, later, thawed and used for stem cell therapy.
  www.cllinfo.com/Glossary/glossary_S.html

• A relatively undifferentiated cell in any tissue responsible for replenishing cells lost from a tissue through normal wear and tear, in the case of adult stem cells, or responsible for virtually all of a fetus's cells, in the case of embryonic stem cells; characterized by being able to replicate (through mitosis) seemingly for ever, either in the body or in tissue culture, without wearing out the ends of the chromosomes. ...
  www.jansen.com.au/Dictionary_SU.html

• an immature cell that has the potential to generate new stem cells and to mature into many different cell types in the organs of our bodies. Early embryos contain stem cells that can develop into any type of cell in the body, but even the mature nervous system contains cells that have the capability to generate new nerve and glial cells.
  www.themiamiproject.org/x168.xml

• A stem cells is a cell from the embryo, fetus or adult that has capability to reproduce itself. It can give rise to specialized cell that make up the tissues and organs of the body.
  www.ebioinfogen.com/stem_gloss.htm

• Undifferentiated, primitive cells in the bone marrow with the ability both to multiply and to differentiate into specific blood cells. [See Genomics: Cloning: Stem Cells]
  www.cs.uu.nl/people/ronnie/local/genome/s.html

• population of cells-ancestors possessing a high proliferation potential and ability to differentiate into different line cells, when in a body, they can turn into any cells of the organ and when in an embryo they can turn into any cell of the body.
  www.stvolkletki.ru/eng/dict/s.html

• A cell that has not yet differentiated, or become a specific type of cell. Stem cells have the capacity to become many different kinds of cells (like a muscle cell, a skin cell, a blood cell, etc.).
  hganj.org/Glossary.htm

• an undifferentiated cell whose daughter cells may differentiate into other cell types (such as blood cells)
  wordnet.princeton.edu/perl/webwn

• Stem cells are undifferentiated cells which have the unique potential to produce any kind of cell in the body and self-renewal capacity. Medical researchers believe stem cells have the potential to change the face of human disease by being used to repair specific tissues or to grow organs.
  en.wikipedia.org/wiki/Stem_cell