Aeon is an element seen in Ace Combat 3: Electrosphere that is used for air purification, creating an 'aeonsphere' over a place with high pollution like big cities. An example of places with an aeonsphere include Port Edwards, Megafloat and the underground city Geofront.
The prototype aircraft X-49 Night Raven has its performance increased thanks to the amount of Aeon in the air. This fact can be noticed on the mission Self Awareness (JP version) when the AI pilot Nemo and Cynthia must destroy the Aeon generators around Port Edwards to decrease the Night Raven's agility. Another example of this fact can be seen during the mission Sole Survivor (JP) when Simon hacks the Aeon generator of Geofront to allow Nemo and Fiona to gain an advantage over the Night Raven .
Also, the laser cannon of the X-49 Night Raven is extremely powerful because of the utilization of the Aeonsphere. Because of this, its power output can be raised to extreme levels.
Aeon originally means "life", and/or "being", though it then tends to mean "age", "forever" or "for eternity".