Final answer:
Keratin is an example of an intermediate filament, a type of cytoskeletal protein important for maintaining cell shape and structure.
Step-by-step explanation:
Keratin is an example of an intermediate filament protein. Intermediate filaments are a diverse group of cytoskeletal elements that include several types of fibrous proteins, with keratin being particularly well known for its role in strengthening hair, nails, and the skin's epidermis. These filaments are important in maintaining cell shape and structure, as they resist tension, linking cells to each other and anchoring organelles within the cell.