AR coating is an optical coating applied to the surface of the lens to reduce reflection.
AR is especially important if you wear high index lenses, as high index lenses reflect more light than regular plastic lenses. Without anti-reflective coating, high index lenses cause more distracting reflections that will make your eyes tired at the end of the day.
AR coating on your glasses will also make your lenses look thinner as your lenses will produce less glare. In addition AR coating is very beneficial when taking photographs while wearing your glasses – AR coating will ensure that your eyes are seen on the picture and not a reflection from your lens.