Question: what is a stem cell?

Tríona O'Connell answered on 11 Nov 2014:

A stem cell is a type of cell that can become another type of cell. Some stemcells can become any type of cell at all. Most stem cells can only become a certain set of cells, for example, haematopoetic stem cells live in your bone marrow and can become any type of blood cell but they can never become a kidney cell.