The document defines and describes four medical terms related to the integumentary system: ichthyosis, onycholysis, rhytidectomy, and sebaceous cyst. Ichthyosis is a scale-like skin disorder characterized by dry, thickened skin resembling fish scales. Onycholysis is a nail disorder involving the spontaneous separation of the nail plate. Rhytidectomy is a type of cosmetic surgery to remove facial wrinkles. A sebaceous cyst is a blocked gland or duct containing fatty secretions under the skin.