There are two basic types of stem cells: embryonic and adult. The controversy of late is about the use of embryonic stem cells. We are interested in adult stem cells, which are naturally occurring in the body.
All stem cells are capable of dividing and renewing themselves for long periods of time, and can give rise to specialized cells. According to the National Institutes of Health, stem cells have the remarkable potential to develop into many different cell types in the body.
When a stem cell divides, each new cell has the potential to either remain a stem cell or become another type of cell with a more specialized function, such as a muscle cell, a red blood cell, a skin cell, etc. Stem cells are the repair system for the body. Theoretically, stem cells can divide without limit to replenish other cells as long as a person or animal is alive.