A soldier is a person who has enlisted with, or was drafted into, the armed forces of a sovereign country and has undergone training and received equipment to defend that country or its "interests". Soldiers usually act in strictly hierarchical societies called armies. Infantry 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 Royal Air Force Regiment of Great Britain (technically they are airmen not soldiers), and members of the United States Marine Corps, Royal Marine of Great Britain, 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.
A pre-modern soldier is also called a warrior, often with the additional qualities of valour and honour, proclaimed by himself or by his peer.