An army (from Latin Armata "act of arming" via Old French armée), in the broadest sense, is the land-based armed forces of a nation. It may also include other branches of the military such as an air force. Within a national military force, the word Army may also mean a field army, which is an operational formation, usually made up of one or more corps.
In several countries the army is officially called the land army to differentiate it from an air force called the air army, notably France. In such countries, the word "army" on its own retains its connotation of a land force in common usage. The current largest army in the world by number of active troops is the People's Liberation Army of China with 2,250,000 active troops and 800,000 reserve personnel.
A field army is composed of a headquarters, army troops, a variable number of corps, and a variable number of divisions. A battle is influenced at the Field Army level by transferring divisions and reinforcements from one corps to another to increase the pressure on the enemy at a critical point. Field armies are controlled by a General or Lieutenant General.
A particular army can be named or numbered to distinguish it from military land forces in general. For example, the First United States Army and the Army of Northern Virginia. In the British Army it is normal to spell out the ordinal number of an army (e.g. First Army), whereas lower formations use figures (e.g. 1st Division).
In the Soviet Red Army and the Soviet Air Force, "Armies" were actually corps-sized formations, subordinate to an Army Group-sized "front" in wartime. In peacetime, a Soviet army was usually subordinate to a military district.