“But when you do find one, your whole world changes, and you don't quite see it again the same way after that.” Unicorns are called unicorns because they’re considered fairly rare in swinger communities, where the term originated, Stewart says. “There are many different types of possibilities, from casual one-night stands to friends with benefits to long-term nesting,” says sexologist Marla Renee Stewart, MA, co-author of The Ultimate Guide to Seduction and Foreplay and sexpert for Lovers. Those in the non-monogamous community, however, have a different (but equally magical) concept of what a unicorn is: It’s a person who is sexually and/or romantically involved with a couple.Ī unicorn may be someone who joins a couple for a threesome for one night, or it may be someone who regularly dates or even lives with both members of a couple. For many, the word “unicorn” conjures images of horse-like creatures with fancy rainbow manes and sparkly horns.