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.