What is "general of the air force"

The General of the Air Force (abbreviated as GAF) is a five-star general officer rank and is the highest possible rank in the United States Air Force. General of the Air Force ranks immediately above a general and is equivalent to General of the Army in the United States Army and Fleet Admiral in the United States Navy. The rank has only been held once in history, by General Henry H. Arnold, who served as head of the United States Army Air Forces during World War II.