Also known as the hieros gamos, the Sacred Marriage is the perfect union of male and female within alchemy to create a spiritually and physically perfected whole. Or at least a whole that approaches the perfect, since some alchemists would say that the only perfect being is the Christian God.
Carl Jung avidly studied historical alchemy since he related the terms and beliefs in alchemy to his own beliefs about the inner mind, the female soul or anima, the male soul or animus, the sub-conscious, the shadow self, the death wish or Thanatos. Modern writers can be expected to be influenced by Carl Jung’s concepts. After all, psychologists and psychiatrists write prolifically in mostly ordinary language while alchemists wrote in code.
The term Sacred Marriage can also refer to the (usually sexual) union of two gods. In Wicca, the Sacred Marriage is the symbolic combination of the Goddess and the God (or her Consort) as a dagger is placed into a chalice. Sometimes, with full mutual consent, the High Priestess and High Priest have sex to ritually represent the Goddess and the God.