Here's why:

* Differentiation is the process by which a cell becomes specialized to perform a specific function. For example, a muscle cell, a nerve cell, or a skin cell.

* Undifferentiated cells are the opposite - they haven't yet committed to a specific type of cell. They retain the potential to become many different types of cells.

Stem cells are special because they can:

* Self-renew: They can divide and create more stem cells, maintaining a pool of undifferentiated cells.

* Differentiate: Under the right conditions, they can be triggered to become specialized cells.

There are different types of stem cells, with varying differentiation potential:

* Totipotent: Can develop into any cell type, including the placenta (e.g., early embryonic stem cells).

* Pluripotent: Can develop into any cell type in the body, but not the placenta (e.g., embryonic stem cells).

* Multipotent: Can develop into a limited number of cell types (e.g., adult stem cells found in bone marrow).

Let me know if you'd like to learn more about a specific type of stem cell!