What does 69 means?

The "69" sexual position is one of simultaneous cunnilingus/fellatio (e.g. mutual oral sex). The 6 and the 9 are symbolic of a person (the rounded portion representing a person's head). Combined they represent two persons in a sexual position facing each other on opposite ends. This position provides both persons easy access to each other's sexual organs.
69: The number after 68 and the number before 70.