I get this question quite often, so I thought I’d answer here with my understanding of it.
In my coaching, I tend to use the term Conscious Sexuality. This is because the word “sacred” seems to me to separate sexuality in terms of the acts that occur - meaning that people think of sacred sexuality being a specific way of love-making: sculptured positions from the kama sutra, or breathing practices and chanting. While these practices can definitely be included in elevated sexuality, they are not necessary.
Its also important for me to share that one way of connecting sexually is NOT more spiritual than another. Whips and handcuffs can become an elevated spiritual practice as much as the missionary position, and sex between strangers as spiritually uplifting as sex between two married people.
What makes sexuality “sacred” is the consciousness of those participating. When we have the intention of presence, honesty, love, and growth within our motivations, the act of sex is sacred.
Within this consciousness we are able to activate our bodies into elevated states of bliss, and our spiritual consciousness grows and expands as well. Within the act of sex and bringing our bodies pleasure, altered states of consciousness can be accessed, much like what happens during the use of plant medicines or deep meditation.
And, worth noting, that the act of sex is so powerful that it can often make a sacred moment out of something quite benign, spontaneously activating one or both (or all) those involved into an other-worldly awareness.
I personally believe that sex in and of itself is a spiritual practice, in that bringing our bodies pleasure is a great act of self-love, and self-love is spiritual. We are on earth to have the experience of a physical body - and we ought to learn the many ways of caring for it. Allowing the body to be a portal to delicious and ecstatic higher consciousness states is a beautiful way to learn and develop ourselves as spiritual beings.