In its most basic form, it is defined as honest consensual non-monogamy. While some decline to allow that Swinging
is part of PolyAmory, the basic definition still applies. You will find, though, that there are as many definitions of PolyAmory as there are people practicing it. PolyAmory must have as a basic more than 2 people in the relationship. Not all participants need be involved with every other participant, nor is co-housing a requirement.
PolyAmory incorporates PolyAndry (many husbands), PolyGyny (many wives), PolyFidelity
(no outside relationships), "open" or "closed" to new partners, fidelitous or not, and many variations of the above.