Polyamory is where people can have more than one romantic relationship at a time. (Where Monogamy is one romantic relationship at a time.)
There are as many different kinks of polyamory as there are polyamorous people.
FAQ:
Don't you get jealous? Some people do. But you work to figure out why and fix the issue. Jealousy isn't a problem it points out that there is a problem.
Isn't that cheating? No, everyone involved knows about everyone else that is the key difference between being poly and being a cheater.
So there is no cheating in poly? No, if you don't tell your partner, or break rules you and your partner(s) all agreed to, you cheated.
A few key terms:
Hierarchical relationship - one where each partner has a primary partner who has primacy, usually referred to as the primary partner. This partner could for example "veto" secondary partners.
Non-Hierarchical relationship - Don't believe in "ranking" partners
Primary-The primary partner in a hierarchical relationship
Paramour-a lover. a.k.a. a partner, a significant other
Metamour-a partner of a lover
Polycule - Poly family map
New Relationship Energy (NRE) - the excitement that comes with a new relationship