Stem cells are unspecialized cells that have two defining properties: the ability to differentiate into other cells and the ability to self-regenerate.

The ability to differentiate is the potential to develop into other cell types.

Totipotent stem cell (e.g. fertilized egg) - can develop into all cell types including the embryonic membranes.

Pleuripotent stem cell can develop into cells from all three germinal layers (e.g. cells from the inner cell mass).

Cells can be oligopotent, bipotent or unipotent depending on their ability to develop into few, two or one other cell type(s).

Self-regeneration is the ability of stem cells to divide and produce more stem cells. During early development, the cell division is symmetrical i.e. each cell divides to gives rise to daughter cells each with the same potential. Later in development, the cell divides asymmetrically with one of the daughter cells produced also a stem cell and the other a more differentiated cell.

Stem cells are the building blocks of various organs and tissues in the body. Stem cells have the remarkable potential to develop into many different cell types in the body. Serving as a sort of repair system for the body, they can theoretically divide without limit to replenish other cells as long as the person or animal is still alive. 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, or a brain cell.