Polyamory is consensual non-monogamy between two or more people, where all parties involved are knowledgeable of each other's existence, and open communication is present across all relationships.  This means that everyone involved has agreed to allow each other to date, have sex, and cultivate meaningful relationships with multiple people.

Polyamory is a broad term that can be used to describe many different types of relationships.  Other terms used for these relationships include: polyfidelity, open marriages, open relationships, open dating, friends with benefits, triads, quads, vees, and communities. It is not uncommon for someone to have multiple partners and to be in very committed relationships with each of them.  Polyamory is not group sex, it's not kink, it's not swinging or sleeping around.  Polyamorous and monogamous people can do those things if they want to, but those are separate from polyamory.

Polyamory challenges the notion that in order to give more love to one person, you must give less to another.  Yet love is not a finite emotion; there is a never-ending amount to give. As Spike Jonze said in the movie Her:

“The heart is not like a box that gets filled up; it expands in size the more you love.”