The Scout in Age of Empires is an early, fast unit primarily used for exploration. It has minimal offensive capabilities and little armor, although it is fast enough to escape combat taking little damage. Its line of sight is very large, making it most effective as a border patrol unit rather than being used for direct assault. It can also, at a pinch, be used as a sneak attack unit, utilising its speed to get in, deal damage and escape before reinforcements arrive, although with its lack of armor it is very vulnerable to enemy fire, especially ranged attacks. It can be trained from the Stable. The line of sight of this unit is upgraded for every age that is researched.
Most players will not use the scout as their explorer until they reach the Tool Age because the players in Age of Empires do not start the game with any of these cavalry units, and instead use a Clubman or a Villager for exploring during the Stone Age. Unlike other cavalry units, Scouts do not get an attack bonus when attacking infantry. It was also the only military unit that wouldn't attack Villagers/non-military ships on his own even if diplomacy status is set to "Enemy". This was changed in update 9 in the Definitive Edition.
"An important innovation in military tactics was the provision of skirmish, or light, troops that scouted ahead of the main body when an army was on the move. While it was important to form solid, disciplined ranks of spearmen or other infantry for the shock of hand-to-hand combat, these dense formations were vulnerable to surprise. It was the function of scouts to keep the army commander informed of the tactical situation and locate enemies so the main body was brought into combat at the right place and time. At the Battle of Kadesh in 1275 BC, Rameses II of Egypt did not investigate reports that the Hittite army was far to the north. Instead he advanced one of his four divisions across the Orontes River and was attacked while his second was still crossing. Rameses managed to win the battle, but the lack of proper scouting put his army in jeopardy."