Quick Answer: Infantry, or infantryman are a type of soldier who specialize in ground combat, typically fighting dismounted. Historically the term was used to describe foot soldiers, i.e. those who march and fight on foot. In modern usage, the term broadly encompasses a wide variety of subspecialties, including light infantry, irregular infantry, heavy infantry, mountain infantry, motorized infantry, mechanized infantry, airborne infantry, air assault infantry, and naval infantry. Other subtypes of infantry, such as line infantry and mounted infantry, were once commonplace but fell out of favor in the 19th century with the invention of more accurate and powerful weapons.