In the world of polyamory, a unicorn is a person who is invited into an existing couple to date and play with. The couple can make demands but the unicorn cannot do anything that could cause any inconvenience for the couple.

What does it mean to be a unicorn in bed?

Typically a sex unicorn is a bisexual woman who agrees to join a pre-existing heterosexual marriage as a third sexual component, without presenting any threat of infidelity or emotional burden to either the husband or wife.