The expression “20/20” and equal portions (for example, 20/40, 20/60, and so forth.) are visual keenness estimations. They are also called Snellen parts, named after Herman Snellen, the Dutch ophthalmologist who built up this estimation framework in 1862. In the Snellen visual keenness framework, the Snellen portion’s maximum number is the review separation between the patient and the eye graph. In the United States, the break is typically 20 feet; it is 6 meters in different nations.
The ability to see the last line on the visual chart (kept at 20 feet or 6 meters) is defined by terminology 6/6 (standard), 6/9 (one line less than 6/6), 6/12 (2 lines less than 6/6). Do you need a spectacle power to read that 6/6 line? If no- then it is unaided or Plano, meaning without needing glasses, you can read the 6/6 line- that is normal.
Some cannot read this line and need to be given spectacle powers, to supplement power makes you read that 6/6 line is what is prescribed to you as best-corrected vision. So, someone may read that 6/6 line needing only a small number like 0.5 D, and someone may need as high as 10 D (just an example).
Some patients cannot read the last 6/6 line and fall short of it and can read the 6/9 or 6/12 line no matter how hard the doctor/ optometrist tries to refract. Assuming that this is correctly done, if you are reading 6/12, it merely means 2 lines less than expected (it may need spec power to read to 6/6).
Only your optometrist can tell you if you can read better till 6/6