Anti-Glare coating, aka anti-reflective coating, is a coating which reduces the amount of light reflecting on the surface of the lens. There are many benefits to having this coating applies to your lenses but the glare reduction is most noticeable during night time driving and computer use.
Though most commonly applied to clear lenses on both sides of the lens, a backside only anti-glare coating is found on most performance sunglasses. Backside anti-glare coatings reduces the amount of light which can bounce off the back surface of the lens and back into the wearers eyes.
Other benefits of Anti-Glare coatings:
Greater visibility of the eyes behind the lens (Makes for better eye contact)
Increased scratch resistance (Premium AR coatings only)
Anti-Static and Oleophobic properties reduce the need to clean the lenses (Premium AR coatings only)
Hydrophobic property reduces fogging (Premium AR only)
Increased visual acuity
Can make the lenses seem "invisible"
Though it is impossible to completely eliminate the reflection of light, it can be reduced. In Ex.1 you'll see two frames; one with and one without an AR coating. Both lenses have reflections but the coated lens has significantly less.
There are many different manufacturers and just as many price points; not to say that you have to go for the highest price point but the premium quality coatings (normally with higher cost) tend to do the best with diffusing glare and reflections.
On the surface it may seem like all AR coatings are the same but there are actually different types.
Ex.1: Top lenses are not coated. Bottom lenses coated with a premium AR coating
Standard Anti-Glare: Best for glasses that are worn all day, inside and out. Typically has the least amount of color and performs especially well during low light conditions such as night driving.
Blue Light: Easily distinguishable by its pinkish-blue hue, Blue Light coatings help to reduce glare but also create some by intentionally "bouncing off" undesired blue light. Best for computer glasses.
Backside: Primarily found on sunglasses, and especially performance sunglasses, backside AR reduces the amount of light that can bounce off the back of a lens and back towards the eyes. Many premium backside AR coatings also have a special anti-UV layer which limits the amount of UV that can bounce back towards the eyes also.