polyfi could be any number of people included and there are technical exceptions too.
We are basically poly-fi.
The three of us (myself, husband and boyfriend) are a poly family with our kids.
But husband is free to find another partner if he wants and has filtered through a few over the years.
The key for us is that we agree to discuss new potentials before adding them.
E, the lady Dh dated for 2 years, she was more fluid and open and none of us cared if she had other lovers (which she did). She had at least 2 couples and a live in boyfriend that were steady and frequently dated outside of that group.
The "rule" or boundary we had regarding her was that DH and she had to use protection always AND she agreed that anytime she had sex with someone new OR her other partners did, she got STI testing and let us know.
BUT-that didn't change the fact that we are still basically poly-fi.
Try to take yourself off this topic for a minute-consider a word like "runner". What is the definition of a "runner". Do you have to run at a certain speed? Certain distance? Certain times per week? What is it that makes a person a runner?
I think you will see that there is a lot of 'wiggle room' in that example; and that is true for MOST words in our language.
Even in the mono world, there are many who consider themselves mono-but they have affairs (so they have sex with multiple partners)
or they are secretly in love with their best friend their whole lives (so they have multiple love partners)
or they have any number of random exceptions to the rule, like "it's ok if it's Brad Pitt or Angelina Jolie".
Don't assume you have to pick the strictest or most lenient definition of a word.