A unicorn 🦄 or unicorning in a relationship refers to a person entering a polyamorous relationship to participate in sexual escapades with a couple. In other words, the sex unicorn joins a couple either for threesomes or to enter into a triad polyamorous relationship.

What do couples call a unicorn?

The term unicorn in dating refers to an individual who is willing to join an existing relationship. This is going to become a romantic partner who will have sex and become romantically involved with both members of the original relationship. Often, the unicorn in question is going to be a bisexual woman.