A four-star rank is the rank of any four-star officer described by the NATO OF-9 code. Four-star officers are often the most senior commanders in the armed services, having ranks such as (full) admiral, (full) general, or (in the case of air forces with a separate rank structure) air chief marshal. This designation is also used by some armed forces that are not North Atlantic Treaty Organisation (NATO) members.
The four-star rank is reserved in Australia for the Chief of the Defence Force, the highest position in peace time.
In times of major conflict, the highest ranks are the five-star ranks: admiral of the fleet, field marshal, and marshal of the Royal Australian Air Force.