A throuple is a relationship involving three people. Polyamory is a broader approach to relationships that allows multiple romantic connections with the knowledge and consent of everyone involved. A throuple can be polyamorous, but not every polyamorous person is part of a throuple.
The key difference
“Throuple” usually describes the number and structure of people in one relationship. “Polyamory” describes a relationship philosophy or practice that can include different structures, including triads, networks, or people who date independently.
Some throuples have a close three-person relationship. Others have different levels of connection between partners. There is no requirement that every relationship look identical.
What they have in common
Both require consent, honesty, communication, and clear boundaries. Nobody should be pressured into a label, a pace, or an agreement that does not work for them.
Read what is polyamory, what is a throuple, and how to set boundaries in a throuple.