Milites were the trained private footsoldiers of Rome. These men were the non-specialist regular soldiers that made up the bulk of a Legion's numbers. Alongside soldiering, they also performed guard duties, labour work, building and other non-combat roles. Milites would usually have to serve for several years before becoming eligible for training to become immunes and thus become specialists with better pay.
The Latin term eventually became synonymous with "soldier", a general term that, in Western Europe, became associated with the mounted knight, due to the fact that they composed the professional military corps during the Early Medieval Era. The same term, however, could design the infantry soldier (Milites Pedites). Other usages include the "Milites Templi", referring to the Knights Templar or Milites Sancti Jacobi (Order of Santiago).
From the Latin root "Miles" derived words such as "Military" and "Militia".