What is the medical term for a thickened or hardened area of skin caused by friction or pressure?

The term that refers to a thickened or hardened area of skin caused by friction or pressure is "callus." Calluses typically develop on areas of the skin that experience repeated stress or friction, such as the hands and feet, as a protective response. This thickening occurs as the outer layer of skin, known as the stratum corneum, proliferates to shield underlying tissues from damage or irritation.

Keratoma refers specifically to a type of skin growth that is usually associated with keratin, but it is not a general term for thickened skin caused by friction. Dermatitis is a term used to describe inflammation of the skin resulting from various causes, such as allergens or irritants, and it does not specifically refer to a thickening effect. Psoriasis is an autoimmune condition that results in rapid skin cell turnover and leads to the development of scaly patches, which is distinct from the thickening due to friction or pressure seen in calluses. Thus, "callus" is the most accurate term for this condition.