Anti-glare coating is made of a very hard thin film that is layered on the lens. It is made of material that has an index of refraction that is somewhere between air and glass. This causes the intensity of the light reflected from the inner surface and the light reflected from the outer surface of the film to be nearly equal.
When the anti-glare coatings are also applied to the front of prescription eyewear, and the purpose of this anti-reflective coating is to reduce the amount of glare that reflects off your lenses.