Aero rims are pretty much anything other than box rims that come standard on lower end bikes. Box rims are U-shaped in cross section. Aero rims have a V-shape to them.
http://www.bikepro.com/products/rims/campy.html has examples of box and aero rims.
P.S. don't worry about feeling ignorant. If I hadn't broke my spokes I wouldn't have a clue.