An individual who desires relationships with more than one more person; people who are in relationships that involve more than two people – a polyamorous relationship.
Polyamorous people identify as polyamorous, and typically seek out other polyamorous people, or people open to polyamorous relationships (even if they themselves are not polyamorous) to form relationships with.
This is not the same as cheating: polyamory is based on informed consent – that is, that everybody involved in the relationship is aware; this could be an open relationship (where individuals involved are free to explore sexual and/or romantic relationships elsewhere), committed relationships which involve more than two people (e.g. a relationship with and between three people), or relationships in which one or both members have other relationships outside of that relationship.
As such, polyamorous relationships can be diverse.
Not to be confused with polysexual.