The term was originally coined by Sigmund Freud in describing his theory of psychosexual development. Specifically, he used the term to describe the unfocused nature of pleasure-seeking in infancy, in contrast to the genital-focused (heterosexual) sexuality of the typical adult.
Over time, however, this colorful term has been lifted out of Freud's often silly, sexist psychoanalysis and acquired broader, colloquial meaning. Herbert Marcuse appears to have started this trend when, in Eros and Civilization, he employed the term to illustrate the goal of "sexual liberation": that is, a liberation of sexual intimacy and pleasure from the bounds of marriage, reproduction, gender, or other normative boundaries. Early gay radical activists took Marcuse's message, and the phrase, and ran with them.
As the sexual revolution faded and the queer rights movement got bigger and more moderate, the term became increasingly the property of cultural conservatives, who deployed it against harbingers of cultural decay from Jerry Springer to the Clintons. (See, e.g, here and here.) It is, of course, a particular favorite of Ann Coulter. It's irresistible, really, conflating as it does sex education, premarital sex, homosexuality, nonmonogamy, sadomasochism, pornography, and everything else that makes them feel nauseated and strangely aroused into one alliterative phrase.
In light of all this, I need hardly explain why this was the perfect name for this blog, which primarily will discuss the full range of human sexual variation as it plays out in the law. But please, don't confuse this blog with another, similarly named one on Blogger (<--not a work-safe link).