An army (from Latin arma "arms, weapons" via Old French armée, "armed" (feminine)) or ground force is a fighting force that fights primarily on land. In the broadest sense, it is the land -based military branch, service branch or armed service of a nation or state. It may also include aviation assets by possessing an army aviation component. In certain nations, the term army refers to the entire armed forces of a nation (e.g., People 's Liberation Army). Within a national military force, the word army may also mean a field army. They differ from army reserves who are activated only during such times as war or natural disasters.
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 Ground Force of China with 1,600,000 active troops and 510,000 reserve personnel followed by the Indian Army with 1,129,000 active troops and 960,000 reserve personnel.
By convention, irregular military is understood in contrast to regular armies which grew slowly from personal bodyguards or elite militia.
