A soldier is a person who has enlisted with, or has been conscripted into, the armed forces of a sovereign country and has undergone training and received equipment to defend that country or its interests. In most countries, the term soldier is limited to such people who serve in the land branch of the armed services (usually known as the army). Armies are strictly hierarchical societies, and within them, groups of soldiers are usually divided into military units of some kind.

A soldier is not necessarily a warrior. Although all soldiers get basic combat training, many soldiers serve in the rear in non-combat positions (such as in office management, clerical, logistics, or research and development positions).

In an army, the most common military rank held by soldiers is the lowest - in the British Army and United States Army, a private or equivalent. In some countries of the world, soldier specifically refers to members of the army who are not holders of an officer's commission. In most armies of the world a soldier who is not an officer can in theory work their way through the ranks to obtain a commission.

A soldier who no longer serves in the armed forces is called a veteran, a term which can also apply to a long-serving or experienced soldier who is still in the army.

Classification

Infantry, or archaically foot, are soldiers who specialize in ground combat. Not all soldiers are infantry, and not all infantry are soldiers. Infantry that are not soldiers include members of the RAF Regiment of the United Kingdom (technically they are airmen not soldiers), and members of the United States Marine Corps, Royal Marines of the United Kingdom, or other marine forces (who are marines not soldiers; in fact many marines bristle at being called soldiers). Finally, many navies maintain naval infantry, who are sailors not soldiers.

Cavalry, or archaically horse, are traditionally soldiers who fight from horseback, but now usually crew armoured fighting vehicles. Variations include dragoons, lancers, hussars and cuirassiers.

Artillery crew heavy weapons.

Engineers, also called pioneers, are military construction and clearance specialists.