20/20 vision is a term used to express normal visual acuity, which is the clarity or how sharp your vision is, measured at a distance of 20 feet. The size of the letters on the standard eye chart is based on work done by the Dutch ophthalmologist, Herman Snellen, in the 1860’s. As a general guideline, if you have 20/20 vision, this means you can see at 20 feet what normal people see at 20 feet. If you have 20/80 vision, this means that you must be at 20 feet to see what normal people would see at 80 feet.
Some people actually have better than 20/20 vision. For example, if someone has 20/15 vision, this means that that person could be at 20 feet to see an object whereas normal people would have to be at 15 feet to see the same object.
Does 20/20 mean perfect vision? No, it only indicates how sharp your vision is. Peripheral vision (the area of vision around you), eye coordination, depth perception, color vision and focusing ability all contribute to your overall visual ability.