Stem cells are immature tissue precursor cells that have the capacity to self-renew and differentiate into multiple different cell types. They can be found in the embryo, as well as in several fetal and postnatal (adult) organs and tissues. 
Characteristics of stem cellss Stem cells have two important characteristics that distinguish them from other types of cells.

Self-renewal - the ability to go through numerous cycles of cell division while maintaining the undifferentiated state.

Plasticity - under specific physiologic or experimental conditions, they can be induced to become specialized cells such as the beating cells of the heart muscle or insulin-producing cells of the pancreas.