You searched for: “keratinization
1. The development of or conversion into keratin; as in the development of a horny layer of tissue.
2. A process occurring in vertebrate epidermis and epidermal structures in which keratin replaces the cytoplasm of a cell.

An example of keratinization is the cornified outer layer of the epidermis of the skin that consists of dead horny cells.

Hairs and finger-toe nails also consist of keratinized cells.