The Key Periosteal Elevator (5/8") is a surgical instrument designed for use in dental and orthopedic surgeries. The "Key" refers to the specific style or brand of the periosteal elevator, while the "5/8"" indicates the width of the blade at the tip, which is 5/8 inch. This instrument is used to lift or separate the periosteum (the connective tissue layer that covers bones) during surgical procedures.