An undifferentiated cell that can divide to become any different type of cell, such as a skin or muscle cell, is called a stem cell. Stem cells are unspecialized cells that have the ability to differentiate into many different cell types, depending on the signals they receive. This ability makes them useful in medical research and therapies, as they can be used to regenerate damaged tissue and treat diseases. There are two main types of stem cells: embryonic stem cells, which are derived from early-stage embryos, and adult stem cells, which are found in adult tissues.