Explanation:

Stem cell is an undifferentiated cell of a multi-cellular organism which is capable of giving rise to indefinitely more cells of the same type and from which certain other kinds of cell may be formed by the cellular differentiation.
They are found in multi-cellular organisms. In mammals, there are two broad types of stem cells: embryonic stem cells and adult stem cells.
Both are generally characterized by their potential to differentiate into different cell types. For e.g. Pluripotent stem cells have the ability to differentiate into almost all cell types.
In the stem cell treatments new adult cells are introduced into the damaged tissue to treat the disease. Stem cells offer new potentials for treating diseases such as diabetes, and heart disease.