PolyFidelity
A relationship structure of 3 or more individuals who have no sexual or loving connections outside the group. This group may be open or closed to new additions, but there is no sexual or loving connections with the new addition until added.
PolyFidelity is a subset of PolyAmory. The Kerista commune of San Francisco used the term extensively in the early 1980's and may have used it from their inception.
polyfidelity
A group in which all partners are primary to all other partners and sexual fidelity is to the group. More primary partners can be added with the entire group's consent. Coined by the Kerista Commune.
The polyfidelity group in which everyone is equal and will decide to allow a new member together.
Polyfidelity
Like polygamy but you don't have to be married.
I'm with Sandy and Anna. But it's not infidelity it's polyfidelity.