For polyamorous couples, the OPP is pretty much what it sounds like, according to Dr. Eric Sprankle, professor of clinical psychology at Minnesota State University, Mankato, and author of DIY: The Wonderfully Weird History and Science of Masturbation.
“It’s when a couple, most typically a man and a woman couple, have (or want to have) some form of open relationship but have a rule that no other men are allowed to be a part of the relationship,” he says. "There can be as many vulvas added to the relationship as desired, but there shall be only one penis."
Read the full article and interview here: