Polyamory
Polyamory is the expansion of romantic relationships beyond two people with the consent and knowledge of all parties involved. More information can be found at polylove.life.
It can also be used to describe an orientation or your desired relationship structure.
Its use in two contexts is similar to how monogamy is used.
"We're in a polyamorous relations" describes the structure of relationships.
"I'm polyamorous" describes your orientation towards the type of relationship you seek.
Polyamory is often shortened to "poly" or "polyam".
When used as a reference to relationship structures, polyamory is a subset of multigamy (or ethical non-monogamy).