It is equivalent in concept to a flag officer in navies and a general officer in armies and marine corps. However, in the British Armed Forces, while an air commodore is an air officer, his Royal Navy equivalent, (Commodore), is not considered a flag officer, nor is his British Army or Royal Marines equivalent, (Brigadier), considered a general officer. However, in 1919 when the RAF introduced its air officer ranks, the equivalent Army rank was brigadier-general which was a general officer rank. The British rank of brigadier was not introduced until 1922.
In some other countries, most notably the armed forces of the United States, army, air force and marine corps, 1 star officers are considered to be general officers and 1 star officers of the navy and coast guard are considered to be flag officers.