Sanpaku gan or Sanpaku (三白) is a Japanese

Japanese language

is a language spoken by over 130 million people in Japan and in Japanese emigrant communities. It is a member of the Japonic language family, which has a number of proposed relationships with other languages, none of which has gained wide acceptance among historical linguists .Japanese is an...

 term that means “three whites” and is generally referred to in English as "Sanpaku eyes". The term refers to the iris

Iris (anatomy)

The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel , grey, violet, or even pink...

 being rather small, so that it can only cover about two-thirds or less of the vertical of the eye; imagining an eye as divided into four portions, the iris only 'colours' one portion, thus leaving the other three in white, hence "three whites".
When the bottom part of the white part of the eye known as the sclera

Sclera

The sclera , also known as the white or white of the eye, is the opaque , fibrous, protective, outer layer of the eye containing collagen and elastic fiber. In the development of the embryo, the sclera is derived from the neural crest...

 is visible it is referred to as 'Yin Sanpaku' by the Chinese.