The Kinsey scale, also called the Heterosexual–Homosexual Rating Scale, is used in research to describe a person's sexual orientation based on their experience or response at a given time. The scale typically ranges from 0, meaning exclusively heterosexual, to 6, meaning exclusively homosexual. In both the male and female volumes of the Kinsey Reports, an additional grade, listed as "X", was used to mean "no socio-sexual contacts or reactions".
https://en.wikipedia.org/wiki/Kinsey_scale