The right answer is Specialized cell (or differenciated cell).
A specialized cell has a whole series of activated genes that contribute to its well-defined identity.
For example, an epidermis cell is a specialized cell: it produces keratin and divides into other epidermal cells ... its precise function, as well as its shape, its lifespan ....
In animals, once the cell is specialized, in general it is definitive! It is the plants, each cell can lose its specialization is becoming undifferentiated.