An army is a large, organized group of soldiers trained and equipped to fight on land during wars or conflicts. Unlike a navy, which fights at sea, or an air force, which fights in the sky, an army specializes in ground combat: marching across terrain, defending territory, and engaging enemy forces in battle.

Armies have existed for thousands of years, evolving from ancient warriors with spears and shields to modern soldiers with advanced technology. The Roman army conquered much of Europe through disciplined training and superior tactics. George Washington led the Continental Army to victory in the American Revolution. Today's armies include infantry soldiers, tank crews, engineers, medics, and specialists who work together as a coordinated force.

The word can also describe any large, organized group working toward a common goal. You might hear about an army of volunteers cleaning up after a natural disaster, or an army of ants marching across a kitchen counter. This usage emphasizes the size, organization, and shared purpose of the group, even when no actual military is involved.

In many countries, the army is one branch of the armed forces, working alongside the navy, air force, and sometimes the marines or coast guard to protect the nation.