Answer: The correct answer is- a cell from which a new cell that has a specialized function is formed.
Stem cells can be described as the undifferentiated cells ( with no specific function) in the body that develop into specific cell type ( such as muscle cell, neurons that have specialized function) through a process of differentiation.
They are found in adults ( in certain tissues like bone marrow, blood, and adipose tissue) as well in the developing embryo ( can be extracted from the inner cell mass).
They play significant role in the repair of damaged tissues ( as new cells with specific functions can be produced from them), also involved medical therapies ( for example transplantation of bone marrow) and other areas.