The average visual acuity for humans is 20/20. While 20/25 vision is below average, it isn't considered low vision. Visual acuity is a rating of "clearness" of vision, so 20/25 vision is slightly blurrier than average. Low vision is classified as between 20/60 and 20/200.
A visual acuity rating of 20/25 means that a person can see something clearly at 20 feet away that a person with average vision can see clearly at 25 feet away. While 20/25 measures how clear vision is at a distance, other aspects such as depth perception, peripheral vision, focusing ability and eye coordination are also important in determining how good a person's vision is.