What is 20/25 vision? What does it mean? Is it better or worse than 20/20 vision?
The correct answer has already been given by several people (namely that this standard of measurement compares the viewer (who stands at 20 feet) with the "normal" person .
If the viewer is very near sighted, the first line he can read off the chart is so large that the "normal" viewer can read it from a lot further away (for example 20/200. This means that the nearsighted person has to get really close to the chart - 20 feet) to see what normals see at 200 feet.
The reason 20 feet is used as the standard, is because, at this distance, the lens of the eye (which can provide additional focus) is maximally relaxed. At this distance, the lens can do nothing to contribute to overall acuity. (This is also why, after doing a lot of close work, people are advised to look into the distance. Looking afar allows the lens (which was working very hard to help with reading) the opportunity to relax.
Acuity of 20/25 is still quite good. Drivers must have at least 20/40 acuity
Most people who have difficulty seeing distant objects without glasses can be corrected to 20/20 with lenses-even those with 20/800 vision .
A person is considered to be legally blind if the best correctable acuity is 20/200.