Embryonic stem cells are special cells derived from early-stage embryos, typically around 3 to 5 days old. These cells are unique because they have the ability to develop into any type of cell in the body, making them pluripotent. This means they can potentially become heart cells, nerve cells, or any other cell type, which is crucial for research and potential medical therapies. Scientists study embryonic stem cells to understand how cells develop and to explore treatments for various diseases. For example, they may help in regenerative medicine, where damaged tissues or organs can be repaired or replaced. However, the use of these cells raises ethical questions regarding the source of the embryos.