The Kinsey scale is a sexuality scale that was developed by Alfred Kinsey, an American biologist and sexologist, when he realized that most people couldn't be strictly characterized as straight or gay. The Kinsey scale ranges from zero to six, with zero being strictly heterosexual and six being strictly homosexual. It isn't a test, but a self rating scale, wherein most people rate themselves between one and five. Individuals who could be described as being asexual have a rating of X on the Kinsey scale.
The Kinsey scale is officially known as the Heterosexual-Homosexual Rating Scale.