Light infantry refers to two different types of units depending on whether referring to Age of Empires III or the expansions The WarChiefs and The Asian Dynasties.
Age of Empires III 
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In Age of Empires III, all ranged infantry units that counter heavy infantry and light cavalry with their ranged attacks are considered light infantry. There is no unit in Age of Empires III that has a direct attack bonus against light infantry, but they are still easily countered by artillery and melee cavalry (heavy), and some heavy infantry in melee mode. That is because light infantry units share a similar set of statistic values such as low hit points, low hand attack and ranged resistance, which makes them vulnerable to melee and siege units. Examples for light infantry units in Age of Empires III are:
- Skirmisher
- Strelet
- Cassador
- Longbowman
- Crossbowman
- Abus Gun
- Jaeger
- Tupi Blackwood Archer
- Seminole Sharktooth Bowman
- Carib Blowgunner
- Inca Bolas Warrior
The WarChiefs Edit
In the first expansion the definition of light infantry changes drastically. In The WarChiefs, light infantry units are infantry units who have 6 speed and more (exception the Rodelero). Light infantry in The WarChiefs can therefore be considered a substitute unit type for cavalry of which Aztecs do not have any. Therefore, light infantry is countered by heavy infantry. The only light infantry units in the first expansion are therefore:
Coyote Runner are a substitute unit type for hand cavalry, so they are also countered by ranged cavalry. Eagle Knight are a substitute unit type for ranged cavalry, so they are also countered by long-range infantry.
All units formerly tagged as light infantry are no longer considered as such. Technically units like the Skirmisher are only defined as ranged infantry or long-range infantry. The only unit type that makes former light infantry units different from units such as Musketeers or Highlanders is the heavy infantry tag they do not own.
The Asian Dynasties Edit
The second expansion continues to use the light infantry definition from The WarChiefs with a minor change: Light infantry units are now selected expansion infantry units with 5 or more speed (except the Rodelero). The complete list of light infantry units in The Asian Dynasties is:
