Cornification is a term used in biology to describe the process by which skin cells become hard, flat, and packed with a protein called keratin. This process forms the protective outer layer of skin and is important for resisting damage from environmental factors. Synonyms for cornification include keratinization, epidermal differentiation, and cornified envelope formation. Keratinization specifically refers to the developent of keratin, whereas epidermal differentiation describes the different stages of development that lead to cornification. Cornified envelope formation refers to the final stage of cornification where cells become fully flattened and calcium ions are deposited to create a hard, protective barrier.