Final answer:
The "20s" in "20/20 Vision" refer to feet, as this term originates from the Snellen chart used in vision testing where 20 feet is the standard distance for comparing visual acuity.
Step-by-step explanation:
In the term "20/20 Vision," the numbers refer to feet in the English system of measurement. Specifically, this term comes from the use of the Snellen chart in vision tests, which typically sets a standard distance of 20 feet for identifying letters of a certain size. So, 20/20 vision indicates that at 20 feet, you can see what an average individual can see at that distance. People with 20/40 vision, for instance, would need to be at 20 feet to see what a person with normal acuity could see at 40 feet away.