Keratinization is a specific term implying the formation of keratin.

Keratinization is the process where epidermal cells become the dry and rigid, as they move towards the surface of the skin.  Eventually the dead cells slough off.  On the intact penis, the glans and other the other mucosal tissue typically have fewer layers of keratinized cells. Circumcision exposes the glans and inner foreskin to air and abrasion, causing the layer of karatin to deepen significantly.  This process continues throughout a man's lifetime, further desensitizing the penis.  Over time, this diminishes the range of sexual pleasure, and may even contribute to impotence.

Reference: NOHARMM description of keratinization