Easter Eggs are hidden features of a software program that the developers don't usually include in the official documentation. Usually they are harmless, amusing, or give extra functionality to the software.
FA Easter Eggs are fond by holding down the keys CTRL / ALT / SHFT on the right side of the keyboard while choosing Create Quick Mission, Pro Mission Creator, or Play Single Mission. Continue to hold down these keys while selecting planes and you will be able to fly two additional objects, the "Atomic Moth" and the "Quetz." In Pro Mission Creator these keys will let you access an additional page of objects. In the Play Single Mission screen this will unlock and allow you to choose from many additional missions which were designed for the games which FA is based on.
The Atomic Moth and the Quetz have some very unique weapons, and there are a few interesting coop missions created around these objects. Have fun.
