Stem cells are cells that retain the ability to renew themselves through mitotic cell division and can differentiate into a diverse range of specialised cell types.
In a developing embryo, stem cells can differentiate into all of the specialised embryonic tissues. In adult organisms, stem cells and progenitor cells act as a repair system for the body, replenishing specialized cells, but also maintain the normal turnover of regenerative organs, such as blood, skin or intestinal tissues.
Stem cell treatment is an exciting and controversial area of medical science which is gaining attention as a potential cure for many diseases and conditions. Each new development in stem cell technology is under intense scrutiny to see whether it is safe and ethically acceptable. Many countries are fast-tracking stem cell research with new approaches being tested in many countries including South Korea, India, China and Turkey.
The UK's NHS Choices web site provides a report on media coverage of stem cell treatment which is well worth reading.