6 degrees of separation is a pop-culture term and an astrological term. Where does pop-culture come from? The popular nature of it originates from within the culture and in this instance, its originated from astrology -which is ancient. (Perhaps it was the pop-culture of its day, with people casually name-checking Aphrodite and her marriage to weirdo Hephaestus
6 degrees of separation refers to an astrological chart wheel, which has 12 'houses'. From any one of the 12 'houses', you can count (no more than) 6, and 'find' an explanation/illustration of anyone in your life. Your marriage partner? Start from the first 'house', count to 6, look in your 7th 'house'. And so on.
People here have enjoyed the astrological predictions on astroamerica. If you search his site, he explains the origins of 6 degrees of separation. Perhaps much clearer than I have
Its always best to obtain information from multiple sources.
This is the internet. And as much as I too love Jessica Adams, she is not the ultimate decision-maker for all things astrological. She is an amazing astrologer (who predicted Brexit a year ago by the way, along with the thunder storms the night before!!) but she may or may not be educated in the history of astrology. Doesn't take away from her awesomeness though.